Table of Contents
- 1 Vaccine-Preventable Childhood Diseases
- 2 Understanding Vaccine Safety: Immunization Remains Our Best Defense Against Deadly Disease
- 3 First Typhoid Vaccine to Protect Children Proven Effective by NICHD Scientists
- 4 Common Vaccine-Preventable Diseases
- 5 Different Types of Vaccines
- 6 Q & A – Adult Immunizations
- 7 Vaccine Development
- 8 Vaccine Safety
- 9 Vaccines Licensed in the United States
- 10 What You Should Know About Vaccines
What exactly is a vaccination and how does it work? Find everything you need to know about vaccinations and how they fight diseases in adults and children.
Vaccine-Preventable Childhood Diseases
We have record or near record low levels of vaccine preventable childhood diseases in the United States, but that does not mean these have disappeared. Many of the viruses and bacteria are still circulating in this country or are only a plane ride away. That?s why it?s important that children, especially infants and young children, receive recommended immunizations on time. In our mobile society, over a million people each day people travel to and from other countries, including countries where many vaccine preventable diseases remain relatively common. Without vaccines, epidemics of many preventable diseases could return, resulting in increased? and unnecessary? illness, disability, and death among children.
The following vaccine-preventable diseases, not long ago, disabled and killed millions of American children. Thanks to our country?s high childhood immunization coverage levels, these diseases are now very uncommon.
- Haemophilus influenzae type b (Hib)
- Hepatitis A
- Hepatitis B
- Pertussis (whooping cough)
- Rubella (German measles)
- Tetanus (lockjaw)
- Varicella (chickenpox)
Haemophilus influenzae type b (Hib)
Pertussis (whooping cough)
Rubella (German measles)
|A respiratory disease caused by a virus
|Rash and fever for two to three days ( mild disease in children and young adults)
|Birth defects if acquired by a pregnant woman: deafness, cataracts, heart defects, mental retardation, and liver and spleen damage (at least a 20% chance of damage to the fetus if a woman is infected early in pregnancy)
|Spread by coughing and sneezing
|Rubella vaccine (contained in MMR vaccine) can prevent this disease.
|A disease of the nervous system caused by a bacteria
|Early symptoms: lockjaw, stiffness in the neck and abdomen, and difficulty swallowing
Later symptoms: fever, elevated blood pressure, and severe muscle spasms
|Death in one third of the cases, especially people over age 50
|Enters the body through a break in the skin
|Tetanus toxoid (contained in DTP, DT, DTaP & Td vaccines) can prevent this disease.
|A virus of the herpes family
|A skin rash of blister-like lesions, usually on the face, scalp, or trunk
|Bacterial infection of the skin, swelling of the brain, and pneumonia (usually more severe in children 13 or older and adults)
|Spread by coughing and sneezing (highly contagious)
|Varicella vaccine can prevent this disease.
Understanding Vaccine Safety: Immunization Remains Our Best Defense Against Deadly Disease
Understanding Vaccine Safety: Immunization Remains Our Best Defense Against Deadly Disease
by Michelle Meadows
Smallpox and polio have been wiped out in the United States. Cases of measles, mumps, tetanus, whooping cough (pertussis) and other life-threatening illnesses have been reduced by more that 95 percent. Immunization against influenza and pneumonia prevent tens of thousands of deaths annually among elderly persons and those who are chronically ill. As a result, millions of lives have been saved. But don’t let the success of vaccines fool you into thinking we no longer need them. Most vaccine-preventable diseases aren’t gone.
Steve Berman, M.D., president of the American Academy of Pediatrics and a pediatrician in Denver, says he and his colleagues were devastated to recently see an infant die of whooping cough. “This was a case where the family thought the risks of vaccination outweighed the benefits,” Dr. Berman says. The baby was exposed to the disease by two older brothers who hadn’t been vaccinated.
Vaccines contain a weakened (attenuated) or killed (inactivated) form of disease-causing bacteria or viruses, or components of these microorganisms, that trigger a response by our body’s immune system. For example, vaccines stimulate our bodies to make antibodies–proteins that specifically recognize and target the bacteria and viruses against which the vaccines are designed, and that help eliminate them from the body when we encounter them.
Without vaccine protection, we can easily contract and transmit infectious diseases. It may only take one person, whether it’s a family member, a neighbor, or a visitor from another country, to start the spread of a disease. And even immunized individuals can be at risk because no vaccine is ever 100 percent effective for everyone. (See Figure 1, “Recommended Childhood Immunization Schedule, United States, January-December 2001.)
The Food and Drug Administration recommends that consumers arm themselves with the facts about the benefits and risks of vaccines, along with the potential consequences of not vaccinating against certain diseases. According to a Washington state-based organization called Parents of Kids with Infectious Diseases (PKIDS), some parents are shocked to learn that children can die of chickenpox and other vaccine-preventable diseases they hadn’t considered a threat.
Sometimes such reports contain unsubstantiated or inaccurate information and don’t reflect a balanced view of the risks and benefits of a particular vaccine. Most parents believe in the benefits of vaccination, as evidenced by record high childhood vaccination rates, and more and more adults are getting vaccinated against influenza, pneumococcal disease, and tetanus. But some people who need vaccines don’t get them for a variety of reasons, including fear of side effects. Lately, a surge of negative publicity focusing on the risks of vaccines–some of which are unproven or inaccurate–has some wondering whether they do more harm than good. But vaccine experts and the overwhelming majority of health-care providers caution consumers against skipping important vaccinations because of an evening news report or a posting on the Internet.
The FDA’s Center for Biologics Evaluation and Research (CBER) regulates vaccines in the United States, and works with several other agencies, including the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH), to study and monitor vaccine safety and effectiveness. New vaccines are licensed only after the FDA thoroughly reviews the results of extensive laboratory studies and clinical trials performed by scientists, physicians, and manufacturers.
For vaccines intended for wide use in healthy populations such as children, clinical testing with careful safety monitoring typically involves thousands of patients before a vaccine is ever licensed. And after a vaccine hits the market, the safety monitoring continues, as does FDA oversight to assure the highest levels of quality control in the vaccine production process.
“We are always monitoring for evidence that might suggest possible problems with vaccines,” says Karen Midthun, M.D., director of CBER’s office of vaccine research and review. CBER scientists also conduct research to better ensure vaccine safety and to better understand vaccine-related side effects.
A Commitment to Safety
On the surface, it may seem that approaching vaccine safety as a continuous process–always looking into problems and potential problems–implies that vaccines are unsafe. “But it’s actually a reflection of our ongoing commitment to safety, and to assuring the prevention of potentially lethal infectious diseases,” says Jesse Goodman, M.D., M.P.H., deputy director for medicine at CBER. “It’s also the nature of science to seek and implement improvements which make for safer and more effective medical products.”
Since 1996, for example, CBER has licensed several acellular pertussis vaccines. Acellular pertussis vaccines use only parts of the disease-causing bacteria and are associated with fewer side effects than the whole cell pertussis vaccines that had been in use. In 1997, the CDC’s Advisory Committee on Immunization Practices (ACIP) recommended a switch from using the whole cell pertussis component of the diphtheria, tetanus, pertussis (DTP) vaccine to using acellular pertussis vaccines for all five doses in the childhood schedule (see “Recommended Childhood Immunization Schedule”).
The National Institute of Allergy and Infectious Diseases (NIAID) sponsored clinical trials for some of the experimental acellular vaccines. “We set out to develop an improved vaccine that would be as effective as the standard whole cell vaccine but cause less extended crying, fevers, and other side effects,” says Carole Heilman, Ph.D., director of NIAID’s division of microbiology and infectious diseases. CBER scientists also played a critical role by developing methods to evaluate the acellular vaccines, which helped them get to clinical trials faster.
There have been other recent policy changes to improve vaccine safety, including ACIP’s 1999 recommendation to change from the use of oral polio vaccine (OPV) to the inactivated polio virus (IPV). OPV had been highly effective in controlling naturally occurring polio outbreaks, preventing thousands of cases of paralysis a year. But as a live virus, it mutated in extremely rare cases to cause polio itself. Continued use of OPV resulted in about 10 cases of paralytic polio each year among millions vaccinated and their contacts, according to William Egan, Ph.D., deputy director of CBER’s office of vaccine research and review. Switching to the use of IPV eliminated this risk and was appropriate once epidemic polio was controlled.
“There are times when we also take action even when there is just the theoretical potential for harm,” Goodman says. Thimerosal, a mercury-containing compound, had been the most widely used preservative in vaccines. Its use in minute amounts helped to prevent bacteria from contaminating multi-dose vials of vaccines and other medicines, protecting against potentially serious infections. But thimerosal has been nearly eliminated from vaccines because of legitimate and growing scientific concerns about the possible effects of mercury on the nervous system, Goodman says.
“In addition, as the numbers of vaccines used in children has increased, small infants who received every recommended vaccine could be exposed to cumulative doses of mercury that exceeded some, but not all, federal guidelines,” Goodman explains.
Even though there are no convincing data that show harm because of thimerosal in vaccines, the U.S. Public Health Service recommended moving rapidly to vaccines that are thimerosal-free. The FDA encouraged manufacturers to comply and set the highest priority for its reviews of such products, Goodman says. As a result, all recommended pediatric vaccines available are now thimerosal free or have greatly reduced thimerosal contents. In March 2001, the FDA approved a newly formulated version of Tripedia, a diphtheria and tetanus toxoids and acellular pertussis (DTAP) vaccine with only a trace amount of thimerosal.
A Thorough Process
The most common components of vaccines are weakened microbes (disease-causing microorganisms), killed microbes, and inactivated toxins. In addition, subunit vaccines, which only use a part of the bacterium or virus, are increasingly being used.
Manufacturers conduct stringent tests to make sure that cell lines used for producing viral vaccines do not contain adventitious agents (unwanted viruses) such as simian virus 40 (SV40), which was found in some early polio vaccines. These vaccines had been manufactured in kidney cells from simians (monkeys) that harbored SV40. Following its discovery, SV40 was removed from vaccines, and vaccines have been free of the virus since the early 1960s. CBER scientists are developing potentially better methods to detect such infectious agents.
Developing vaccines is a thorough and rigorous process, Egan says. Vaccines are tested for safety on animals first, and then in humans during several phases of clinical trials. The most important clinical trial for the recently licensed vaccine Prevnar involved nearly 40,000 people, equally divided between those who received the vaccine and those who did not. Prevnar was approved to prevent invasive pneumococcal diseases such as meningitis.
A group of FDA scientists reviews data and the proposed labeling of the vaccine, which includes directions for use and information about potential side effects. The committee also reviews manufacturing protocols, conducts its own tests, and inspects the manufacturing facility. The FDA’s Vaccines and Related Biological Products Advisory Committee, which includes scientific experts and consumer representatives, can be consulted at any time to review data and recommend action to the agency.
After a vaccine is licensed, the FDA generally requires that manufacturers use validated methods to test samples from each vaccine lot for safety, potency, and purity prior to its release for public use. The FDA also tests selected lots and products to help assure the accuracy of tests conducted by the manufacturers.
“Most vaccines cause some side effects, but they are usually minor and short-lived like low-grade fever and soreness at the injection site,” Midthun says. Serious vaccine reactions–causing disability, hospitalization, or death–are extremely rare but they can happen.
Like any medicine, vaccines carry a small risk of serious harm such as severe allergic reaction. But experts point out that the risk of being harmed by a vaccine is much lower than the risk that comes with infectious diseases.
For example, in 1976, the swine influenza (flu) vaccine was associated with a severe paralytic illness called Guillain-Barr? Syndrome (GBS). According to the CDC’s vaccine information sheet on the influenza vaccine, “if there is a risk of GBS from current influenza vaccines, it is estimated at 1 or 2 cases per million persons vaccinated, much less than the risk of severe influenza, which can be prevented by vaccination.” Each year, flu causes tens of thousands of deaths, mostly among older people. Most people who get the influenza vaccine have no serious problem from it.
And though some people worry about it, you can’t get the flu from the flu vaccine, Midthun says. “Just as there are no vaccines that are 100 percent safe, there are also none that are 100 percent effective,” she says. “So you may get the flu soon after you received the vaccine, before it could be expected to protect you. It does not mean the shot gave you the flu,” she says.
Some live virus vaccines, such as the chickenpox vaccine, can cause mild versions of the disease they protect against, says Goodman. “But this is usually only a serious problem if the patient has a severely compromised immune system.” And vaccines are generally not advised for such people. It’s important to talk with your doctor about the benefits and risks of vaccines, and any concerns you may have, specifically as it relates to you and your family (see “Steps to Take When You Vaccinate“). If you or your child has previously had a significant reaction to a vaccine, that may affect the risk/benefit ratio for the individual and whether that vaccine should be recommended again.
How Reactions Are Evaluated
Before a vaccine is put into standard medical practice, it must be studied in clinical trials of thousands of people, which allows for evaluation of relatively common side effects. For example, a common side effect might occur in one or more of several hundred vaccine recipients. But rare events (fewer than one case in several thousand recipients) aren’t usually evident in clinical trials. “Unless you’ve studied something in a million or more people, you might never see the very rare event or be able to know whether it occurred due to vaccination or simply by chance,” Goodman says.
Through the Vaccine Adverse Event Reporting System (VAERS), jointly operated by the FDA and the CDC to monitor the safety of licensed vaccines, experts look for patterns and any unusual trends that may raise questions about a vaccine’s safety once it is used more widely in the population. The FDA continuously reviews and evaluates individual reports, in addition to monitoring overall reporting patterns. The FDA also monitors reporting trends for individual vaccine lots. Most reports come from health-care providers, but anyone can report an unexpected event after vaccination to VAERS. (See “Steps to Take When You Vaccinate” for the VAERS toll-free number.)
VAERS receives 800 to 1,000 reports each month. Because it often can’t be determined whether an adverse event occurring after vaccination was actually caused by the vaccination, health-care providers and consumers are encouraged to report any event that might be attributable to a vaccine.
“You don’t have to be sure,” says Susan Ellenberg, Ph.D., director of CBER’s office of biostatistics and epidemiology. “Reporting possible reactions will help identify adverse events that might be truly associated with vaccinations and need further study.” But this approach to reporting means that one can’t assume that all VAERS reports describe true vaccination reactions.
VAERS is a passive, voluntary reporting system, which means not all adverse events get reported. It also means that many reports are incomplete or even contain inaccurate information because the forms are not filled out by trained personnel. Another problem with interpreting VAERS data is the lack of information on the total number of individuals who received a particular vaccine, making it impossible to estimate the incidence of reported adverse events. It’s also often the case that multiple vaccines are given at the same time, further complicating the interpretation of what might have caused the event, Ellenberg says.
Despite these problems, VAERS does contribute in important ways to understanding vaccine safety. VAERS data may suggest the need for more research on certain vaccines. “In this sense, VAERS is a signal generator,” Egan says. Recently, VAERS data were instrumental in evaluating RotaShield, a vaccine licensed to protect against rotavirus infection. Rotavirus is the most common cause of gastroenteritis in children younger than five and can result in severe diarrhea, dehydration, and death. This virus is an especially serious problem in developing nations, where it kills hundreds of thousands of children every year.
Following the vaccine’s licensure, VAERS started to receive reports of bowel obstruction in a number of infants who had received RotaShield. A careful review of these reports revealed that the bowel obstruction occurred most often in the first two weeks after RotaShield was administered. As a result, the CDC recommended postponing any further distribution or administration of RotaShield until more data could be collected and evaluated.
The FDA discussed the concerns with the manufacturer, which decided to voluntarily withdraw the product from use. In November 1999, ACIP withdrew its previous recommendation for universal use of the vaccine. At this time, the FDA, NIH, and CDC are still studying the bowel obstruction and RotaShield-associated cases, Egan says. “We continue to look into mechanisms for any serious adverse events. We want to understand why they happen so that we can prevent them from occurring in the future.”
The CDC’s Vaccine Safety DataLink, which links computerized histories of vaccination to hospitalization records and other medical information for members of eight large managed care organizations, supplements the information in VAERS and permits more rigorous evaluation of possible safety concerns. For example, the system allows researchers to compare how often an adverse event occurs in people recently vaccinated with those not recently vaccinated, to evaluate the likelihood that the vaccine caused the adverse event.
Some have looked to vaccines to explain a host of serious conditions that we don’t fully understand, including sudden infant death syndrome (SIDS), multiple sclerosis, diabetes, and autism. There have been a number of epidemiological studies of these possible associations, and experts say there is no good scientific evidence at this time showing that vaccines cause these diseases or conditions.
“Physicians give vaccines to children at multiple time points during their development and a lot can happen during that time,” says Midthun. She stresses that both the FDA and the CDC take concerns of parents seriously. After careful review of all available information, neither agency has found that existing data support any link between the measles, mumps, and rubella (MMR) vaccines and autism, a hypothesis that has received considerable publicity over the last year.
The CDC and the NIH recently contracted with the Institute of Medicine, part of the National Academy of Sciences, to establish the Immunization Safety Review Committee. The independent committee is charged with evaluating nine vaccine safety topics over a three-year span. The possible association of the MMR vaccine and autism was the first topic.
On April 23, 2001, the Immunization Safety Review Committee reported its finding that the current evidence does not favor the hypothesis that there is a link between MMR and autism and that no changes should be made in the current policy of administering the MMR vaccine. The committee could not rule out the possibility that the MMR vaccine might be linked to autism in some sub-population and recommended that targeted research in this area be conducted. To date, there is no indication as to whether there is any such subpopulation, or what the genetic makeup or other characteristics of such a subpopulation would be, Egan says.
“It’s important that policy decisions about vaccine safety be based on science,” says Martin G. Myers, M.D., director of the U.S. Department and Health and Human Service’s National Vaccine Program Office. As vaccine safety research continues, Myers says, we can’t afford to lose sight of what life was like before immunization. Vaccination is the reason we don’t see the suffering, disability, and death from whooping cough, measles, polio and other infectious diseases like we used to.
“Vaccines are very safe,” Myers adds, “but nothing is without risk.” Not vaccinating against certain diseases means choosing another type of risk, he says. Myers recalls treating an infant with seizures from tetanus so strong they shook the baby’s whole body. These types of seizures and many deaths are preventable by vaccination. And Myers still has an audiotape from the early eighties of a child hacking and gasping for air because of whooping cough. “The child’s mother asked me to play it for parents who might be undecided about getting vaccinated.” He’s also played the tape for medical students and residents. “It doesn’t take long before somebody in the room asks me to please turn it off.”
National Vaccine Injury Compensation Program
The National Vaccine Injury Compensation Program became effective in 1988. The program is a federal “no-fault” system designed to compensate those individuals, or families of individuals, who have been injured by childhood vaccines. A claim may be made for any injury or death thought to be the result of a vaccine covered under the program. The program is administered jointly by the U.S. Department of Health and Human Services, the U.S. Court of Federal Claims, and the U.S. Department of Justice. For more information, call 1-800-338-2382, or visit www.bhpr.hrsa.gov/vicp.
Steps to Take When You Vaccinate
- Review the vaccine information sheets that explain the potential risks of each vaccine. Health practitioners are required by law to provide them.
- Talk to your doctor about whether certain reactions to vaccines can be controlled. For example, fever may be prevented or reduced by taking acetaminophen before or after vaccination.
- Tell your doctor if you, your child, or a sibling has ever had a bad reaction to a vaccine.
- Ask your doctor about conditions under which you or your child should not be vaccinated. This might include being sick or having a history of certain allergic or other adverse reactions to previous vaccinations or their components, such as allergies to eggs, which are used to grow influenza vaccines.
- Report unexpected events after vaccines to your doctor and to the Vaccine Adverse Event Reporting System (VAERS) at 1-800-822-7967.
First Typhoid Vaccine to Protect Children Proven Effective by NICHD Scientists
Scientists at the National Institute of Child Health and Human Development (NICHD) have developed and tested the first vaccine capable of protecting children from ages 2 to 5 against typhoid fever. Results of the study, which was conducted in Vietnam, appear in the April 26 “New England Journal of Medicine”. The effectiveness of the vaccine — 91.5 percent — is the highest reported for any typhoid vaccine.
“We have a two-fold victory in world public health,” said Duane Alexander, M.D., Director of the NICHD. “Not only is this the first vaccine to protect young children against typhoid fever, it appears to be the most effective typhoid vaccine ever developed. And in contrast to other typhoid vaccines, it is virtually free of side effects.”
Untreated, typhoid fever is a debilitating and life-threatening illness caused by the bacteria, “Salmonella typhi”. Vaccine development for typhoid fever has been difficult because “S. typhi” inhabits and causes illness only in human beings — there are no animal models for the disease. Typhoid fever is spread by fecal contamination of drinking water or food, or by person to person contact. The disease is common in developing countries lacking adequate sewage and sanitation facilities. Symptoms include fever, stomach pains, weight loss, loss of appetite, delirium, severe diarrhea (in children), and constipation (in adults). According to the U.S. Centers for Disease Control and Prevention, about 16 million people worldwide develop typhoid each year, and 600,000 die from it. Roughly 400 cases of typhoid fever occur in the U.S. each year, about 70 percent of which are acquired by Americans traveling abroad. (Thyroid fever)
The NICHD researchers chose to do the study in the Dong Thap province of the Mekong Delta, a rural area which lacks a public sewage system and therefore has a high incidence of typhoid fever-roughly 413 cases for every 100,000 children under age 15. More than 90 percent of the typhoid strains present in the area are resistant to the antibiotics used to treat the disease.
In developing the vaccine, the NICHD researchers used an approach they had earlier pioneered. The approach involves chemically linking a polysaccharide from the disease-causing bacteria with a protein molecule. Ordinarily, the polysaccharide would slip past the defenses of a child’s immature immune system. But adding the protein to the polysaccharide allows the immune system to produce antibodies that inactivate the bacteria. Antibodies are immune system proteins that recognize a particular substance. Together with another protein called complement, antibodies begin the first steps in the complex sequences of events by which the immune system destroys disease-causing organisms.
Two of the researchers, Dr. John Robbins and Dr. Rachel Schneerson, received the prestigious Pasteur and Lasker Awards for using this approach to develop a vaccine that virtually eliminated disease caused by the deadly and debilitating bacteria, “Haemophilus influenzae” type B (Hib), from the developed world. (http://www.nichd.nih.gov/new/releases/cviawar2.htm). Hib vaccination also is being implemented in Africa, South and Central America, and in Southeast Asia. Dr. Robbins is the recipient of this year’s Albert B. Sabin Gold Medal for dedicating his career to preventing diseases that afflict children, such as meningitis, pertusis, typhoid, and several others.
In all, 11,091 Vietnamese children ranging from age 2 to age 5 took part in the study. The children received two injections, 6 weeks apart. Half received the vaccine, and the other half, a placebo. In the following two years, both groups were observed by their physicians throughout the study. Those who developed typhoid fever received the standard treatment of antibiotic therapy for the disease. “S. typhi” was isolated from only 4 children who had received both injections of the vaccine. The placebo group had 47 cases, for an effectiveness rate of 91.5 percent. By comparison, typhoid vaccines currently on the market have a 70 percent effectiveness rate and do not protect children under age 5 against the disease. Fewer than 2 percent of children experienced any side effects, all of which were mild, and limited to swelling at the injection site, or to mild fever that resolved within 48 hours.
The study authors wrote that they next plan to test the vaccine in children under two, to see if it can be administered at the same time as the routine vaccination for Diphtheria, Tetanus, and Pertussis. Because of the high levels of protective antibodies the vaccine brought about in young children, the study authors also wrote that the vaccine would probably be at least 90 percent effective in individuals above 5 years of age, “including the military and travelers to areas with high rates of typhoid fever.”
Authors of the study were Feng Ying C. (Kimi) Lin, M.D., M.P.H, Zuzana Kossaczka, Ph.D., Delores A. Bryla, M.P.H., John B. Robbins, M.D., Rachel Schneerson, M.D., and Shousun C. Szu, Ph.D, all of the National Institute of Child Health and Human Development, NIH; Joseph Shiloach, Ph.D., National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Vo Anh Ho, M.D., Phan Van Bay, M.D., Mai Ngoc Lanh, M.D., Dong Thap Province Hospital; Ha Ba Khiem, M.D., Tran Cong Thanh, M.D., Pasteur Institute, Ho Chi Min City; and Dan Duc Trach, M.D., Ph.D., National Institute of Hygiene and Epidemiology, Hanoi.
Common Vaccine-Preventable Diseases
The following diseases are preventable through vaccinations:
- Hepatitis A
- Hepatitis B
- Hib disease
- Pertussis (whooping cough)
- Pneumococcal pneumonia
- Rubella (German measles)
Different Types of Vaccines
When a new disease emerges or a familiar one becomes a more significant health threat than it has been in the past, scientists, physicians and public health workers recognize the need for a new way to prevent the disease. Once scientists have identified the organism or toxin that causes the illness, they pursue a number of approaches to develop a vaccine.
Vaccine development has its early roots in the work of Edward Jenner, who discovered how to protect people from smallpox, and Louis Pasteur, who developed a vaccine to protect from rabies. Those pioneering efforts subsequently led to vaccines for diseases that had once claimed millions of lives worldwide.
The purpose of a vaccine is to bring about active immunity by provoking a response from a person’s immune system—marshaling B and T cells to swing into action—and creating a memory within the immune system so that exposure to the active disease agent will stimulate an already primed immune system to fight the disease. Some vaccines are combinations that protect against several diseases. Most of us are familiar with the DTP (diphtheria, tetanus, pertussis) and MMR (measles, mumps, rubella) vaccines that children in the United States receive. Scientists extensively test these combination vaccines to make sure that none of the antigens detracts from the immune priming effect of the others. Thus the vaccines can provide triple protection, the recipients are spared extra needle sticks, and the public health costs are reduced.
Based on the biological and chemical characteristics of the disease-causing agent and on what type of immunity is desired, researchers begin to develop one of the following types of vaccines. Vaccines can be produced from 1) inactivated (killed), 2) live, attenuated (weakened), or 3) synthetic (laboratory-made) microbial materials.
Inactivated vaccines are produced by killing the disease-causing microorganism with chemicals or heat. Such vaccines are stable and safe; they cannot revert to the virulent(disease-causing) form. They often do not require refrigeration, a quality that makes them accessible to the people of many developing countries, as well as practical for vaccinating people who are highly mobile, such as members of the armed forces. However, most inactivated vaccines stimulate a relatively weak immune response and must be given more than once. A vaccine that requires several doses (boosters) has a limited usefulness, especially in areas where people have less access to regular health care. The flu shot is an inactivated vaccine, as are the vaccines for cholera, plague, and hepatitis A.
Live, Attenuated Vaccines
To make a live, attenuated vaccine, the disease-causing organism is grown under special laboratory conditions that cause it to lose its virulence, or disease-causing properties. Although live vaccines require special handling and storage in order to maintain their potency, they produce both antibody-mediated and cell-mediated immunity and generally require only one boost, or additional dose. Most live vaccines are injected; some, however, such as the polio vaccine, are given orally. In addition, intranasal vaccines, administered in the nose, show promise in preventing flu.
While there are advantages to live vaccines, there is one caution. It is the nature of living things to change, to mutate, and the organisms used in live vaccines are no different. There is a remote possibility that the organism may revert to a virulent form and cause disease. It is for this reason that live vaccines continue to be carefully tested and monitored.
For their own protection, people with compromised immune systems—such as people who are taking immunosuppressive drugs, people who have cancer or people living with HIV—are usually not given live vaccines. The vaccines for yellow fever, measles, rubella, and mumps are all produced from live, attenuated organisms.
A toxoid is an inactivated toxin, the harmful substance produced by a microbe. Many of the microbes that infect people are not themselves harmful. It is the powerful toxins they produce that can cause illness. For example, the bacterium that causes tetanus is found everywhere in nature, and in an environment with plenty of oxygen, it is harmless. If that same organism is put into an environment without oxygen, however, the organism starts to change and produce tetanus toxin, a substance far more potent than the well-known poison sodium cyanide. To inactivate such powerful toxins, vaccine manufacturers treat them with materials known to completely cripple any disease-causing ability. Formalin, a solution of formaldehyde and sterile water, is most often used to inactivate toxins and produce toxoids. Toxoids are used to immunize people against tetanus and diphtheria.
New and Second-Generation Vaccines
Scientists are using new technologies to improve traditional vaccines. These new second-generation vaccines, as well as vaccines for diseases that had not been preventable very long ago, are made using powerful techniques such as recombinant genetic engineering (also called recombinant DNA technology).
The bacteria that cause some diseases, such as pneumococcal pneumonia and certain types of meningitis, have special outer coats. These coats disguise antigens so that the immature immune systems of infants and younger children are unable to recognize these harmful bacteria. In a conjugate vaccine, proteins or toxins from a second type of organism, one that an immature immune system can recognize, are linked to the outer coats of the disease-causing bacteria. This enables a young immune system to respond and defend against the disease agent.
Currently, conjugate vaccines are available to protect against a type of bacterial meningitis caused by Haemophilus influenzae type b (Hib). Meningitis, an inflammation of the fluid-filled membranes that protect the brain and spinal cord, can be fatal, or it can cause severe, life-long disabilities such as deafness and mental retardation. Since Hib vaccines have been in widespread use in the United States, Hib meningitis has nearly disappeared among babies and young children.
Sometimes vaccines developed from antigenic fragments are able to evoke an immune response, often with fewer side effects than might be caused by a vaccine made from the whole organism. Subunit vaccines can be made by taking apart the actual microbe, or they can be made in the laboratory using genetic engineering techniques. Today, subunit vaccines are used to protect against pneumonia caused by Streptococcus pneumoniae and against a type of meningitis.
A recombinant subunit vaccine for hepatitis B virus infection is now licensed for use in the United States. The recombinant vaccine is made by inserting a tiny portion of the hepatitis B virus’ genetic material into common baker’s yeast. This process induces the yeast to produce an antigen, which is then purified. The purified antigen, when combined with an adjuvant, a substance that stimulates the immune system, results in a safe and very effective vaccine.
Recombinant Vector Vaccines
A vaccine vector, or carrier, is a weakened virus or bacterium into which harmless genetic material from another disease-causing organism can be inserted.
The vaccinia virus, the virus that causes cowpox, is now used to make recombinant vector vaccines. In the submicroscopic world of viruses, vaccinia is relatively large and has ample room to accept additional genetic fragments. A vaccinia virus with several genes from the human immunodeficiency virus (HIV) is currently being tested as a vaccine for acquired immune deficiency syndrome (AIDS). In addition, a close relative of vaccinia, canarypox virus, engineered with harmless fragments of HIV, is being tested in human volunteers as a vaccine for AIDS.
Similarly, scientists are testing a weakened bacterium—salmonella—to carry portions of such microbes as the hepatitis B virus. Currently no recombinant vector vaccines are licensed for general use in the United States.
Q & A – Adult Immunizations
by Gregory A. Poland, MD, FACP
Q. What vaccines are available to protect adults?
A. Immunizations are readily available for such common adult illnesses as influenza (flu), pneumococcal disease and hepatitis B. Vaccinations against measles, mumps, rubella (German measles), hepatitis A, tetanus, diphtheria, and chickenpox are also needed by some adults. Public Health Service recommendations identify people at risk who need these shots.
Q. Should all adults be immunized?
A. Yes. As a general rule, all adults require measles, mumps, rubella, tetanus, and diphtheria immunizations. All adults age 65 and older and those with diabetes and chronic heart, lung, liver, or kidney disorders need protection against influenza and pneumococcal disease. Hepatitis B vaccine is indicated for adults in certain high-risk groups, such as healthcare workers and persons with multiple sex partners. Hepatitis A vaccine is recommended mainly for travelers visiting developing countries where hepatitis A is common and clean water and proper sewage disposal are not available; for adults who have a chronic liver disease or clotting-factor disorders; those who use illegal drugs; and for men who have sex with men. Adults who have not had chickenpox should consider getting tested to see if they are immune and if not to get the vaccine.
Q. How often do I need to be immunized?
A. Immunizations for pneumococcal disease (except for patients at particular risk for pneumococcal complications), measles, mumps, and rubella usually are administered once, and may protect you for life. Some persons born after 1956 may require a second measles vaccination. Flu vaccine must be administered yearly due to new strains of virus which are not contained in previous vaccines. After age seven, immunization for tetanus and diphtheria (Td vaccine) must be supplemented with a booster shot every 10 years. Hepatitis B vaccine is administered in three doses given over a six-month period. Two doses of chickenpox vaccine are recommended for persons 13 years and older who have not had the disease. Two doses of hepatitis A are needed 6 to 12 months apart to ensure long-term protection.
Q. Where can I obtain my immunizations?
A. Consult your health care provider or local health department for a list of doctors who administer these shots. Your city or county health department or local hospital may hold clinics to administer these vaccines.
Q. What do these shots cost?
A. The cost may vary depending on insurance coverage. Check with your health care provider or clinic and your health insurance for exact rates. Remember, both the influenza and pneumococcal shots are paid for by Medicare Part B.
Q. Are there side effects to these immunizations?
A. Vaccines are among the safest medicines available. Some common side effects are a mildly sore arm or low fever. As with any medicine, there are very rare risks that serious problems, even death, could occur after getting a vaccine. However, the risks from the diseases are much greater than the risks from the vaccines.
Q. What shots do I need if I’m traveling abroad?
A. Contact your health care provider or health department as early as possible to check on the immunizations you may need. The time required to complete them will depend on whether you need one dose or a vaccine series. Several books provide information on the specific vaccines required by different countries and general health measures for travelers. Call the Centers for Disease Control and Prevention travelers information line at (404) 332-4559.
Q. Should I carry a personal immunization record?
A. Yes! A permanent record should be kept by every adult. It will help you and your health care provider ensure your protection against vaccine-preventable diseases. It can also prevent needless revaccination during a health emergency or when you change providers. Ask your provider for this record. Be sure to take it with you to his/her office so it can be updated each time you receive a shot.
Q. Where can I get additional information?
National Coalition for Adult Immunization
4733 Bethesda Avenue Suite 750
Bethesda, MD 20814-5228
CDC National Immunization Information Hotline
1-800-232-0233 (Spanish Service)
Monday-Friday 8:00am – 11:00pm Eastern Time
National Institute on Aging
PO Box 8057
Gaithersburg, MD 20898-8057
To be approved for general use, a candidate vaccine must go through a long period of testing and validation. The time between discovery of a disease agent and production of a widely available vaccine has been as long as 50 years. Today, with biological synthesis and recombinant vaccine development techniques, the length of time from basic research to availability of a licensed product can sometimes be greatly reduced.
Basic Research and Development
Basic research focuses on biochemistry and physiology and on mechanisms that disease-causing microbes use to cause damage. Such research also takes into account the biophysical characteristics of the organisms that might be used in vaccines or drugs to prevent or interrupt the disease process.
To develop a candidate vaccine, scientists test vaccine preparations in cell-culture, and often eventually in animals such as mice, guinea pigs, or even monkeys. In some cases, computers can help researchers visualize the vaccine candidates in three dimensions to predict how vaccine antigens will interact with the immune system. If the vaccine candidate is shown to be promising throughout the preclinical evaluations, it can become an investigational vaccine.
An investigational vaccine is one that successfully has gone through basic research and developmental processes, often including preclinical trials in animals, and has been approved by the U.S. Food and Drug Administration (FDA) for use in human volunteers in clinical trials.
Clinical studies rely entirely upon the participation of volunteers, people who contribute their time and energy for the advancement of science and improved health care for all. Thousands of volunteers of all ages and from all walks of life have participated in these studies. A typical volunteer in a vaccine study agrees to be given the vaccine, makes frequent visits to a clinic for evaluation, participates in medical testing, and provides blood or tissue samples that will be used in assessing the vaccine’s safety and potential effectiveness. Unlike the boy vaccinated by Dr. Jenner 200 years ago, volunteers today must sign an informed consent document indicating their understanding of the study, its risks, and their willingness to participate.
A candidate vaccine undergoes three phases of clinical trials before it can be licensed for public use. Phase I trials, to determine the safety of various doses of the vaccine, usually begin with small numbers of volunteers, and then expand to include more volunteers if the vaccine appears to be safe.
Phase II trials, to determine whether the vaccine is safe and immunogenic, are open to hundreds of volunteers. The vaccine is tested for safety, for its ability to evoke an immune response, and for its potential to prevent disease.
Phase III trials are large-scale efficacy studies, often in thousands of individuals, to confirm that the vaccine safely prevents disease. A vaccine is considered successful if its overall effect is beneficial; it should prevent disease, and any side effects should be minimal. If the disease the vaccine is designed to prevent is rare in the United States, Phase III trials may be conducted in a country where the disease is prevalent. In the cases of such international cooperation, each government signs an agreement and expects its citizens to benefit from the study.
Side Effects and Adverse Reactions
The most common side effects of vaccines include low-grade fever, soreness and redness at the site of the injection, or sometimes body aches for up to 24 hours after vaccination. These minor side effects of a vaccine are far preferable to having the disease.
The extensive testing that a vaccine undergoes before it is licensed for public use is conducted, in part, to assure safety as much as possible by closely observing large numbers of volunteers for harmful side effects. But no matter how thorough the testing, it is impossible to allow completely for the extensive variation among individuals, their immune systems, and their reactions to the introduction of new substances into their bodies. Serious systemic reactions to vaccines can occur, although they are very rare. The FDA and the Centers for Disease Control and Prevention monitor vaccine distribution and use. Information about adverse reactions to a vaccine is collected even after the vaccine is licensed for general use. Both organizations record any incident of a serious reaction and follow up on any re-evaluation of the vaccine that is necessary.
Vaccines of the Future
Currently scientists are pursuing many promising new strategies in vaccine development and exploring novel ways to administer vaccines. The following descriptions of just a few of these innovative ideas provide a preview of safer, more effective ways to fight disease.
Exposing mucosal membranes to vaccines is a strategy that can produce an immune response in a less-stressful and better targeted manner. Mucosal membranes are located throughout our bodies, but are most accessible in the lungs, nose, mouth, throat, gastrointestinal tract, rectum and vagina. The oral polio vaccine, in use since the 1950s, is an early example of the effectiveness of this strategy. Another possible mucosal route of administration is through the nose, and flu vaccines may soon be widely available in a nasal spray. Researchers have shown that the route of entry a disease-causing organism takes is often an effective vaccine route as well. Many vaccine improvements may result from progress in designing better adjuvants. At present, only an aluminum salt called alum is approved as an adjuvant by the FDA, but scientists are studying many new natural and synthetic compounds.
Scientists are also looking at new ways of presenting the vaccine to the immune system. Microspheres, tiny spheres containing bits of antigenic material, show promise in that they can release small doses of vaccine over extended periods of time as the microspheres gradually dissolve in the body. This means that someone may be able to receive two or three doses in just one administration of vaccine.
Perhaps the most exciting new vaccine technique is introducing pure genetic material directly into the body. This genetic material, called “naked DNA,” encodes a few proteins from a disease-causing organism. The DNA is then incorporated into the body’s own cells, which make the proteins encoded by the new DNA. It is these proteins that are recognized as foreign and stimulate the immune system. In this way, the DNA will have an effect similar to that of a live, attenuated vaccine. In effect, the DNA will produce antigens for years and induce strong, long-lasting immunity. At the same time, the exclusion of genes that are critical to the disease-causing organism’s survival will assure that the vaccines are safe and do not actually cause disease.
Researchers are also exploring ways to create edible vaccines. By genetically engineering plants to incorporate synthetic antigens, scientists may be able to develop a banana or potato, for example, that will produce protective immunity when eaten. Obviously, such a vaccine technique would greatly simplify immunization for many people of the world.
Vaccines remain among the most powerful tools we have for disease prevention, and advances in biotechnology have ushered in a new era in vaccine development that holds even more promise for improving public health. NIAID remains a leader in the discovery and testing of new and improved vaccines and will continue to nourish this exciting renaissance in vaccine development.
- The safety record on vaccines
- Vaccine risks
- How vaccine safety is tested
- How vaccine safety is monitored
- Parents have a role in vaccine safety, too
- In the rare event that something goes wrong: The National Vaccine Injury Compensation Program (VICP)
Vaccines are very safe. Today, the United States has the safest, most effective vaccine supply in history. Vaccines have provided Americans with tremendous health benefits, with a minimum of risk. In 1996, almost 81.6 million immunizations were given in the U.S. alone, and many billions more have been given safely around the world.
The prosperity of any nation is directly linked to the health of its population. The widespread availability and acceptance of immunization in America has prevented a huge burden of disease, complications, and deaths from polio, measles, pertussis (whooping cough), tetanus (lockjaw), diphtheria, mumps, and rubella (“German” measles). As recently as 1990, Haemophilus influenza type b was a common, devastating illness and the leading cause of bacterial meningitis in U.S. children. Now, most pediatricians (doctors who specialize in diseases of childhood) just finishing their training have never seen a case, thanks to immunizations.
As with any medical procedure or medication, immunizations are associated with a risk of an adverse reaction. Typical reactions may include warmth, redness, and tenderness at the site of the injection, and irritability. Potential serious reactions vary according to the type of immunization, and include the potential for seizures, damage to the brain or central nervous system, and death. However, most reactions are minor and treatable. There are so few deaths that could plausibly be connected to vaccine, and the risk is so small, that it is hard to assess statistically.(1)
The National Vaccine Program Office supports continuous vigilance, so that any increase in risk from a vaccine is quickly recognized and so that measures can be taken to make vaccines even safer. The CDC National Immunization Program and the Food and Drug Administration (FDA) have systems in place for monitoring reports of reactions. Among these is the Vaccine Adverse Event Reporting System (VAERS), which is described more fully below in the section titled “How Vaccine Safety Is Monitored.”
Vaccines have been so successful in preventing disease in the U.S. that in recent years, the annual number of reports to VAERS have exceeded the total number of reports of routine childhood vaccine-preventable disease. This may lead some people to believe that the vaccines are dangerous. However, based on the very large numbers of data collected nationwide through the various data systems, the risk of a serious adverse reaction to an immunization is extremely small. The risk of the disease itself is substantially more serious than the risk of the immunization.
The U.S. government agency charged with assuring the safety of vaccines in development, vaccines in clinical trials (experimental studies that occur in phases, gradually increasing the number of people involved in testing), and vaccines in use is the FDA.
In general, all vaccines must receive two licenses before being released for marketing: one for the vaccine, and one for the manufacturing plant. It is the FDA that defines the rigorous studies and many documents required to get the license, as well as actually granting or refusing a license. The FDA is also involved in the type of labeling that is done and the information that is given to health care professionals about how to use the vaccine, precautions, known side effects, and other aspects of the vaccine. Once a license is granted, manufacturers may begin producing the vaccine, but they must continuously test each lot of the product for potency, safety, and quality, and the results of these tests must be given to the FDA.
Once a vaccine is in use, physicians must keep very careful records of who receives the vaccine and what lot of vaccine was used. This way, if a problem arises, it is possible to track down the lot that was used, so it can be tested and evaluated to see if the vaccine was at fault.
Administering the vaccine is not the end of the monitoring process. As described by the Institute of Medicine in a 1997 workshop summary,(2) adverse events that may be linked with vaccines are monitored in four ways:
1.The Vaccine Adverse Event Reporting System (VAERS). The National Childhood Injury Act was established in 1986. This law requires health care providers to report any serious adverse events that occur within 30 days after vaccination with any vaccine. The reports must be submitted to VAERS, which was set up in 1990 and is managed by the Centers for Disease Control and Prevention and the FDA. The VAERS system is capable of creating clues that may be useful in uncovering potential new adverse events and any change (increase or decrease) in the rate of reporting of previously known adverse events associated with vaccines. However, it is a “passive” system of gathering data, and therefore may not capture as many events as an aggressive system would. More important, since lot sizes vary and the number of doses within a lot that have actually been given is not known, the raw number of reported adverse events, by itself, does not make it possible to interpret whether there is an actual problem. For example, “three adverse events” may have entirely different meaning if a million doses have been given, versus 30 doses.
Patients, parents, or even non-relatives who witnessed or who are aware of a reaction can also submit a report to VAERS. A copy of the VAERS reporting form and instructions for how to submit it can be obtained by calling 1-800-822-7967.
2. The Vaccine Safety Datalink (VSD). The VSD was established by the CDC in 1990. It links large databases of four health maintenance organizations containing data on a known population size (more than 500,000 children of ages 0 to 6 years, both vaccinated and not vaccinated), in Oregon, Washington, and California. Because this system actively finds cases and systematically reviews medical records from a population of known size, the VSD captures more complete data on adverse events associated with vaccination. The VSD makes it possible to do large epidemiologic studies of vaccine adverse events, captures information on less commonly occurring types of adverse events, and helps determine whether an event is linked with a vaccine or with some other cause.
3. Surveillance by vaccine manufacturers. Manufacturers are required by the National Childhood Vaccine Injury Act of 1986 to report adverse events to the Department of Health and Human Services. (3)
4. Monitoring by the FDA. The FDA monitors adverse events reporting rates, using both the VAERS data and manufacturers’ data. Among the things FDA looks for are large numbers of adverse event reports early in the circulation of a lot, clusters of similar cases, syndromes (groups of symptoms), or other patterns; additional information from other sources with knowledge of a particular case; patterns of reported adverse events linked to final lots filled from the same bulk vaccine; and documentation that lots in question have passed all the required tests.
The VSD and VAERS are complementary methods of monitoring data. VAERS is a signal generator, designed to provide clues that there may be problems with specific lots of vaccine that require more investigation. VSD provides actual incidence rate of diseases and events that occur around the time of vaccination and at times not linked to vaccination, making it possible to evaluate whether the vaccine actually caused the adverse event and, if so, the magnitude of the problem.
Government agencies and vaccine manufacturers have strict guidelines for vaccine safety, but a parent plays a role, too. Here are several things a parent can do:
1. If any aspect of your child’s appearance or behavior gives you concern after a vaccination, report it to your child’s health care provider immediately. Respond to your instincts as a parent. If you feel the situation is an emergency, say so. Write down what happened and the date and time it happened. Ask your health care provider to file a Vaccine Adverse Event Report form or call 1-800-338-2382.
2. Learn the facts about immunizations and infectious diseases. In 1993, a Gallup poll of 1,000 parents of children under five years of age showed a great gap in many parents’ understanding of immunization and infectious diseases: 47% were unaware that polio is contagious, 36% didn’t know that measles can be fatal, and 44% didn’t know that Haemophilus influenza type b was the leading cause of potentially fatal bacterial meningitis, a disease that as recently as 1985 was a major killer of infants and toddlers.
3. Periodically review the Current Vaccines and Recommended Vaccination Schedule, which is posted in the “What’s New?” section of the CDC National Immunization Program’s website. Vaccination schedules are available for adults or children. By following the schedule, you can be sure to get your child’s immunizations at the safest and most advantageous age.
4. Always keep a record of your child’s immunizations, and bring it with you to office visits. This will ensure that vaccines are given on schedule and that your child does not receive excess immunizations. This is especially important if you move, change doctors, or vaccinations are given anywhere other than in your regular physician’s office (for example, if your child is given a tetanus [lockjaw] shot during an emergency room visit).
5. Review the Standards for Pediatric Immunization Practice, which provides guidelines on what your pediatrician or family health care provider should know and do about vaccines.
In the rare event that something goes wrong: The National Vaccine Injury Compensation Program (VICP)
The National Childhood Vaccine Injury Act of 1986 established the VICP. This program went into effect in October 1988 and is a Federal “no-fault” system designed to compensate those individuals, or families of individuals, who have been injured by childhood vaccines, whether administered in the public or private sector. The act covers the following vaccines: diphtheria, tetanus, pertussis (DTP, DtaP, DT, TT, or Td), measles, mumps, rubella (MMR or any components), and polio (OPV or IPV), Haemophilus influenzae type b (HibV), hepatitis B, and varicella (chickenpox). While the act was written with vaccine-injured children in mind, it also applies to any adult who is injured by the vaccines listed above. Complete information on this program is available at the CDC National Immunization Program site.
2. Institute of Medicine, Vaccine Safety Forum, Board on Health Promotion and Disease Prevention. Vaccine Safety Forum: Summaries of Two Workshops. Washington DC: National Academy Press, 1997.
3. Food and Drug Administration, Center for Biologics Evaluation and Research. Vaccine adverse event reporting system [online]. Washington, DC: FDA, 1997. Available at http://www.fda.gov.
Vaccines Licensed in the United States
The following vaccines are licensed in the United States:
- Adenovirus vaccine
- Anthrax vaccine
- Bacille Calmette-Gu?rin vaccine
- Cholera vaccine
- Diphtheria toxoid
- Diphtheria and tetanus toxoids
- Diphtheria and tetanus toxoids and acellular pertussis vaccine
- Diphtheria and tetanus toxoids and whole cell pertussis vaccine
- Diphtheria and tetanus toxoids and pertussis and Haemophilus influenzae b (Hib) conjugate vaccine
- Hib conjugate vaccine (with diphtheria, meningococcal, and tetanus conjugates)
- Hepatitis A vaccine
- Hepatitis B vaccine
- Influenza virus vaccine
- Japanese encephalitis virus vaccine
- Measles virus vaccine
- Measles and mumps virus vaccine
- Measles, mumps, and rubella virus vaccine
- Meningococcal vaccine, Group A
- Meningococcal vaccine, Group C
- Meningococcal vaccine, Groups A and C
- Meningococcal vaccine, Groups A, C, Y, and W-135
- Mumps virus vaccine
- Pertussis vaccine (acellular)
- Pertussis vaccine (whole cell)
- Plague vaccine
- Pneumococcal vaccine
- Poliovirus vaccine—inactivated
- Poliovirus vaccine—live, attenuated
- Rabies vaccine
- Rubella vaccine
- Smallpox vaccine
- Tetanus toxoid
- Typhoid vaccine
- Varicella (chickenpox) virus vaccine
- Yellow fever vaccine
What You Should Know About Vaccines
Disease prevention is the key to public health. Vaccines benefit in particular the people who receive them, and in turn, those people cannot spread disease to others who have not been vaccinated. Infection cannot spread if it never gains a foothold. Infectious diseases cause enormous suffering, strain the capabilities of our health care system, and deplete financial resources. For the individual, the health care provider, and in the interest of conserving human and financial resources, it is always better to prevent a disease than to treat it.
Veterinary vaccines benefit people, too. Some diseases, such as rabies, anthrax, certain types of encephalitis, and Rift Valley fever, are readily transmissible from animal species to humans. In many instances, livestock and pets are vaccinated not only for their own health, but for that of their owners.
In the United States, federal and state public health programs help assure that children receive vaccines. Many childhood diseases that were a normal part of growing up just 50 years ago are now preventable. Measles, rubella (German measles), mumps, pertussis, (whooping cough), and chickenpox were almost unavoidable. Most people did not reach adulthood without their families or circle of friends being touched by a serious illness or death caused by an infectious disease. For the most part, children suffered through the course of the disease and were left with naturally acquired immunity, some school work to catch up on, and perhaps a little pockmark somewhere on their skin. However, in some cases, children died, or they were left with permanent loss of hearing or sight or other tragic effects of serious infections.
Although most of us receive the great majority of our immunizations during childhood, it is important to remember that vaccines are not just for young children. Adolescents and adults should keep up-to-date on tetanus and diphtheria immunizations. Adults who have not had diseases such as measles or chickenpox during childhood, or the vaccines to prevent them, should consider being immunized. Ironically, childhood diseases such as measles, mumps, and chickenpox can be far more serious in adults.
People who travel overseas should determine, together with their physicians or at international travel clinics, which vaccines would be appropriate based on their destinations. Effective vaccines are available to prevent yellow fever, polio, typhoid fever, hepatitis A, cholera, and other bacterial and viral diseases that are more prevalent abroad than in the United States.
Each year, as we prepare for winter and the flu season, many adults should consider the benefits of the flu vaccine. In addition to flu vaccine, immunizations for pneumococcal pneumonia, hepatitis A, and hepatitis B are recommended for people who may be at risk.
Evalutating a Vaccine
Variations in individuals and their immune systems are many and subtle; thus no vaccine is totally effective. In the United States, a vaccine is approved for general use if it fulfills several stringent requirements.
- The vaccine must be safe. Although it is quite unlikely that a vaccine will ever be 100 percent safe, it must produce protective immunity with only minimal side effects (such as redness and soreness at the vaccination site) for the overwhelming majority of those who receive it. More discomfort in side effects can be acceptable, however, depending upon the severity of the disease the vaccine is designed to prevent. For example, most people would consider vaccine side effects that mimicked the symptoms of a bad cold acceptable if the vaccine protected them from HIV disease.
- The vaccine must be immunogenic, that is, it must cause a strong and measurable immune response. Vaccines usually contain antigens, bits of material, sometimes from the disease-causing microbe itself, that can stimulate the immune system to respond and fight off a potential infection. When a vaccine is immunogenic, it primes the recipient’s immune system to recognize the disease-causing microbe and launch a counterattack before illness can occur. In addition, the vaccine must induce the right type of immunity. When microbes invade, they cause disease in different ways, and different parts of the immune system respond to fight them. Vaccines must stimulate the specific parts of the immune system that protect against a particular kind of organism.
- The vaccine must be stable during its shelf life, that is to say, its potency must remain at the proper level for the vaccine to evoke an immune response. Many inactivated vaccines are simple to store, since they are in powdered form and are reconstituted with the appropriate fluid before they are given. Live, attenuated vaccines, however, require refrigeration from manufacturer to clinic to maintain stability and potency.
All approaches to vaccine development focus on the immune system and the body’s natural defenses against foreign invaders. To understand something of how vaccines work, it is best to start with the immune system. Together, your immune system and vaccines are powerful allies in the fight against disease.