What is it?

Overview

What Is It?
A vaccine is designed to stimulate the adaptive immune system before you're exposed to the virus and bacteria so when you do encounter it, your body is ready to spring into action before the pathogen can make you sick.

The discovery and wide application of vaccines that protect against once-fatal childhood diseases like measles, mumps, rubella and diphtheria is one of the most significant medical contributions of the past two centuries. Today, newborns get their first vaccine soon after birth (hepatitis B), then, between one and two months begin a series of shots that will eventually protect them against 14 diseases. Worldwide, childhood vaccines prevent up to 3 million deaths each year and spare more than 750,000 children from serious disability.

Most parents vaccinate their children, with less than 1 percent of children under three years not receiving recommended vaccines. Those figures represent record-high levels of children receiving vaccines. However, children from low-income families, school-aged children and adolescents have lower immunization rates.

Vaccines are not just for kids, however. Adolescents and adults need them, too, whether to "boost" earlier immunizations that provided immunity against diphtheria, pertussis and tetanus or to protect against other diseases, such as influenza, pneumonia, shingles, bacterial meningitis or, for those traveling abroad, yellow fever and typhus. Preteen girls can be vaccinated against several strains of the human papillomavirus (HPV), which cause most cervical cancers. Vaccines are also being developed to prevent malaria and HIV, the virus that causes AIDS, as well as to harness the power of the immune system to fight cancer and other diseases.

The History of Vaccines

The roots of modern vaccines stretch halfway across the world to ancient China and India where, as early as the 10th century BC, people inhaled pus from smallpox blisters to inoculate themselves against the deadly disease. But it wasn't until 1796 that a country doctor from England named Edward Jenner formally vaccinated a child against the disease.

Rather than using pus or scabs from individuals infected with smallpox, he used pus from a similar, but less virulent pox disease called cowpox. He hypothesized this would protect against smallpox because milkmaids infected with cowpox never caught smallpox, even during epidemics. Two weeks after inoculating an 8-year-old boy, Jenner tried to infect him with smallpox. Nothing happened. Voila! The first successful vaccination. (Indeed, the word vaccine comes from the Latin word "vacca" for cow).

It, however, would be nearly two centuries later before smallpox was eradicated worldwide (the last known case occurred in Somalia in 1977). Its banishment (except for samples held in Russian and American laboratories) has been heralded as one of the most significant medical achievements in history.

We've come a long way from Jenner's days, when "vaccines" were given by using a quill or ivory point to transfer the pus from an infected person into a healthy person's skin. Today, safe, hair-thin needles deliver nearly painless injections, while some vaccines can be given orally with drops or nasally through a spray.

Today we have vaccines against childhood illnesses like diphtheria, mumps, rubella and measles, which used to kill millions of children each year; against tetanus and rabies; and even against cancer. Some are designed to protect against infection in the first place; others to prevent the pathogen's replication and halt its ability to infect normal cells. In all, more than 300 approved vaccines protect against 30 diseases. Not only have vaccines saved lives, they have changed the very world in which we live.

Vaccine Basics

To understand how vaccines work, you first need to understand how your immune system works. There are two types of immunity: innate and adaptive . The innate immune system is a nonspecific response to any threat. Invaders such as bacteria, viruses and other pathogens display "signs" on their surface called antigens that signal immune system cells to action.

The innate immune system includes visible protection, like skin and the mucus membranes in your nose and mouth that strain out pathogens; and invisible protection in the form of white blood cells like macrophages, which release inflammatory chemicals such as histamine and leukotrienes to destroy invaders. Sometimes this process runs amok, as when the innate immune system launches an all-out attack against harmless proteins like those from pollen or peanuts, resulting in an allergic reaction.

A more targeted approach to threats comes from your adaptive immune system, which responds to specific antigens. The foundation of this system exists in T and B lymphocytes. These immune cells learn to recognize certain antigens. Once they identify a non–self invader, they generate specific responses to destroy that invader. B cells mature into specialized cells with antigen-specific antibodies on their surfaces that lock onto the antigen to annihilate it. T cells release toxins to destroy the invader or call other immune system cells into action. Once T and B cells are activated, they leave behind copies of themselves that are ready to spring into action again if the specific antigen appears. This is known as immunologic memory.

These mature T and B cells enable your immune system to launch an attack against, say, a measles virus so quickly that the virus never has time to infect healthy cells and make you sick. Thus, the adaptive immune system, unlike the innate immune system, protects against reinfection.

The problem with the adaptive immune system is that the first time it encounters a new antigen it can take several days to get up to speed once it encounters a new antigen. That's more than enough time for most pathogens to replicate and make you sick.

Enter vaccines.

A vaccine is designed to stimulate the adaptive immune system before you're exposed to the virus and bacteria so when you do encounter it, specialized T and B cells already exist, ready to spring into action before the pathogen can make you sick.

Types of Vaccines

Vaccines are produced in several ways.

• Live, attenuated vaccines
• Inactivated vaccines
• Subunit vaccines
• Toxoid vaccines
• Conjugate vaccines
• DNA vaccines
• Recombinant vector vaccines

Live, attenuated vaccines. These vaccines contain a live, although significantly weakened, version of the pathogen. Measles, mumps and chicken pox vaccines are made with live viruses. Few bacterial vaccines are made with live pathogens.

The benefit of a live vaccine is that a single dose often provides lifelong immunity. The downside is that because viruses and other pathogens naturally mutate, or change, the virus within the vaccine could also change, possibly creating a more virulent version of itself that the immune system would have difficulty combatting. This was an issue with the early oral polio vaccines, but is generally not a problem with current live vaccines, which are much safer than the virus they protect against. Only people with a suppressed immune system (such as those who have HIV, are taking immunosuppressant drugs or are being treated for cancer) should be concerned about receiving live vaccines because they could, conceivably, become infected with the virus. Live vaccines also usually require refrigeration.

Inactivated vaccines. These vaccines contain a killed version of the pathogen. They are more stable (meaning they don't need refrigeration) and safer than attenuated viruses, but they don't elicit as strong an immune response. Thus, the immunity they provide may not last as long and you might need a "booster" vaccine down the road.

Subunit vaccines. These vaccines are made with bits and pieces of the inactivated antigen called epitopes. The advantage is that by using fewer molecules of the virus or bacteria, there is less risk of side effects. The disadvantage is that it is challenging and time consuming to identify the exact epitopes needed to stimulate the immune system.

Toxoid vaccines. These vaccines are designed to protect against bacteria that secrete toxins. Treating the bacteria with formalin renders the toxins harmless but still retains enough of their structure to "teach" immune cells to recognize the bacteria and train them to lock onto the toxin antigen before the bacteria can release the chemical. Toxoid vaccines are used for diphtheria and tetanus.

Conjugate vaccines. Conjugate vaccines are typically used to provide protection against certain types of bacterial infection, particularly in very young children. These bacteria, including those that cause bacterial meningitis, are surrounded by a thick capsule called a polysaccharide coating. This coating helps the bacteria hide from the immune system. Thus, antigen-presenting T cells can't "show" the antigen to B cells. B cells can still produce antibodies against the bacterial antigens and provide some protection, albeit short-lived, but this type of protection doesn't develop until children are about 2 years old. So many polysaccharide vaccines for adults and older children don't work in younger children, leaving children highly susceptible to the illnesses those bacteria cause.

Enter the conjugate vaccine. Antigens or toxoids that the baby's immune system does recognize are attached to the polysaccharide coating. The infant's immune system learns to recognize polysaccharide coatings as dangerous and to defend against such pathogens.

DNA vaccines. DNA vaccines are exactly what they sound like: Vaccines made of the organism's genetic material, which carry the code, or recipe, for antigens. Once in the body, normal cells take up the DNA and begin making the microbe's antigens, displaying them on their surface and stimulating the immune system to respond. It's like turning normal cells into vaccine-making machines. Because the vaccine does not contain the pathogen itself, it can't make you sick. No DNA vaccines are currently in use, but some are being tested for influenza and herpes.

Recombinant vector vaccines. With recombinant vector vaccines, the microbe's DNA is inserted into another virus or bacteria that transports the DNA, enters cells and releases the DNA into the healthy cell. Bacterial vectors produce microbial antigens that they display on their surface to provoke the immune response. These vaccines also are not yet approved for widespread use but are being evaluated for HIV, rabies and measles and are thought to be even safer than existing vaccines.

When to Vaccinate

When to Vaccinate

The chart contains recommendations from the U.S. Centers for Disease Control and Prevention for preventive vaccines. Don't panic if you or your child has not received all vaccinations on time; the CDC has guidelines for "catch-up" vaccination that your health care professional should be aware of.

If you are traveling out of the country, make an appointment with your health care professional at least four to six weeks before your trip to see if you need any travel-related vaccines. Travel is also a good time to make sure you're up-to-date on your other vaccines, as well. The only vaccines required by law are:

• Yellow fever: Required for travel to countries in sub-Saharan Africa and tropical South America
• Meningococcal vaccine: Required for travel to Saudi Arabia during the Hajj, an annual pilgrimage

Other travel-related vaccines include typhoid, hepatitis A (for adults not vaccinated as children), Japanese encephalitis vaccine and rabies.

Centers for Disease Control and Prevention Vaccination Recommendations

Centers for Disease Control and Prevention. Possible side effects from vaccines. Available at: http://www.cdc.gov/vaccines/vac-gen/side-effects.htm. Accessed December 19, 2008 .

Truth about Vaccines

Truth about Vaccines

Untruths and myths about vaccines have been circulated for hundreds of years. Complaints and concerns range from invasion of privacy and "bodily integrity" to concerns about safety, the use of animals to prepare and test vaccines and religious issues.

But if only a few people vaccinate their children, vaccines would not be very effective in reducing or eliminating disease. Between 85 to 95 percent of a population must be vaccinated to provide protection for all (herd immunity). That's why most states in the United States require vaccination before children enter school. The Supreme Court has upheld such laws since the early part of the 20 th century. 5

Even today, however, some parents refuse to vaccinate their children. The most recent controversy around vaccines stems from suspicion of a possible link to the rising rates of autism of either the preservative thimerosal, which contains mercury, or the measles component of the MMR (measles/mumps/rubella) vaccine. Parental concern led to numerous scientific investigations regarding such links, with study after study finding no connections. Nonetheless, thimerosal was phased out of most vaccines in 2001. Autism rates, however, have continued to rise.

Vaccines are extremely safe. The Centers for Disease Control and Prevention operates an Immunization Safety Office, www.cdc.gov/vaccinesafety/about/iso.htm, which continuously monitors vaccine safety, including side effects. Part of its mission is managing the vaccine adverse event reporting system, which serves as an "early warning" system to detect vaccine-related problems. For instance, in 1999 the live, oral rotavirus vaccine was pulled from the market one year after approval because of a handful of reports of a rare but serious obstruction of the intestine called intussusception.

About 30,000 adverse event reports are filed annually, but just 10 to 15 percent are classified as serious (causing disability, hospitalization, life-threatening illness or death, though many of the incidents are ultimately not linked to vaccination). Anyone can file a report, including health care providers, manufacturers, personal injury lawyers and vaccine recipients or their parents or guardians.

Children or adults who are harmed by a vaccine may apply for compensation from the National Childhood Vaccine Injury Compensation Fund.

Other vaccine myths and truths:

Myth: The flu vaccine can cause the flu.

Fact: The vaccine cannot cause the flu if you're vaccinated with the inactivated trivalent vaccine, made with killed virus. However, fever and achiness can occur after a flu vaccine. This is not the flu, however, but the repercussions of an activated immune system.

The nasal flu vaccine, which contains a weakened live virus, could, conceivably, cause the flu in someone with a suppressed immune system. Thus, it is only approved for use in healthy people between 5 and 49 years of age (younger and older people tend to have weaker immune systems). Studies involving hundreds of healthy children and adults showed no evidence that the nasal flu vaccine resulted in the flu.

However, you can get the flu after being vaccinated if the viral types used to make the vaccine do not match the circulating flu viruses. These viruses change every year, which is why the vaccine changes every year and why you need an annual vaccine. Nonetheless, in any given year the flu vaccine typically protects 70 to 90 percent of healthy adults under 65. The older you are the less effective it is, likely because of a weaker immune system.

Even when the vaccine and viruses aren't well matched, the vaccine still protects a considerable number of people. Plus, if you get the flu, having had a vaccine means a quicker recovery with fewer complications. And don't forget it takes about two weeks after you're vaccinated before the vaccine fully engages your immune system. During those two weeks, you're still susceptible to an influenza virus, even one the vaccine should protect against.

Myth: Adolescents don't need vaccines.

Truth: Adolescents definitely need vaccines. Children 11 or 12 need the tetanus-diphtheria-acellular pertussis (Tdap) vaccine; the meningococcal conjugate vaccine; the influenza vaccine; and, for girls, the human papillomavirus (HPV) vaccine, which protects against viruses that cause most cases of cervical cancer.

Plus, teens (and adults) who haven't had chicken pox or been immunized against the disease should get a varicella vaccine. It is also very important that adolescents (and adults) get regular boosters for tetanus, diphtheria and acellular pertussis (whooping cough). Unfortunately, while vaccination rates for young children are very good, those for adolescents are far below what they should be. For instance, in 2007 just 72 percent of adolescents ages 13 to 17 were vaccinated with one or more doses of either the tetanus/diphtheria (Td) vaccine or the tetanus/diphtheria/pertussis (Tdap) vaccine.

Myth: Vaccines provide 100 percent protection forever.

Truth: It depends on the vaccine. Most vaccines that children get in their early years provide lifetime immunity. Some, like the influenza vaccine, are required annually because the viruses causing influenza change every year. Others, like the diphtheria-tetanus-acellular pertussis (DTaP) vaccine, require "booster" shots to maintain immunity. For instance, immunity from pertussis (whooping cough) vaccination wears off, making adults and adolescents particularly susceptible to the disease. The bacterial disease can lead to significant time lost from work and school. More worrisome is the fact that it can be transmitted to children who have not been vaccinated, particularly newborns, in whom the disease can be fatal.

Because booster shots are needed in adolescents and adults—who are less likely to get vaccinated than children—pertussis is the only vaccine-preventable infectious disease increasing in prevalence in the United States . In 2005, nearly 26,000 cases were reported to the CDC, the highest in four decades. The number of actual cases is likely triple that . That's why the CDC added a recommendation for the adolescent booster of Tdap in 2005.

Myth: It's OK not to vaccinate your child if other parents vaccinate theirs.

Truth: In our global world, it's important to vaccinate all children. In just the first seven months of 2008, the CDC received 131 reports of measles occurring in 15 states and Washington , DC . Fifteen patients were hospitalized, including four children less than 15 months. Nearly all cases (91 percent) occurred in those who had not been vaccinated, primarily school-aged children, and most originated in other countries, particularly Europe.

High vaccine rates are necessary to provide "herd immunity" (protecting those who have not been immunized). For instance, children under 12 months cannot receive the measles vaccine, so they are particularly vulnerable. Plus, some people cannot be vaccinated for medical reasons; high rates of vaccination in the community help protect them. Measles should not be taken lightly: it is one of the most infectious diseases known to man, able to be transmitted for up to two hours after an infected person has left the room. Before the vaccine became available in the mid-1960s, up to 450 deaths and 4,000 cases of measles-related encephalitis occurred each year in the United States.

Myth: Giving a child multiple vaccinations for different diseases at the same time increases the risk of harmful side effects and can overload the immune system.

Truth: There is no problem vaccinating children for different diseases at the same time. Numerous studies evaluating the effects of combinations of vaccines and of giving children several vaccines at once show this approach is as effective as giving children individual vaccines with no greater risk for side effects. Giving a child two or more vaccines during one health care visit not only provides maximum protection but reduces required office visits, saves time and money and minimizes trauma (from the shots) to the child. There are also combination vaccines, in which multiple vaccines are delivered in one shot.

Therapeutic Vaccines

Therapeutic Vaccines

Cancer Vaccines

When you think of a vaccine, you think of something designed to protect you from a disease. These are called prophylactic vaccines. But vaccines are also being investigated as a way to harness the power of the immune system to fight existing disease, particularly cancer. These vaccines are called therapeutic vaccines.

Cancer cells proliferate for two main reasons: They develop from normal cells, so they don't register as "foreign" to the immune system; and they have developed ways to prevent detection by the immune system. The goal of therapeutic cancer vaccines is to enhance the "foreignness" of the tumor and train the immune system to recognize similar antigens as foreign.

Researchers have several cancer vaccines in late-stage clinical trials, including ones to treat breast and prostate cancer. Click each type to learn more.

Antigen/adjuvant vaccines

Tumor cell vaccine

Dendritic cell vaccines

Idiotype vaccines

Vector-based vaccines

DNA vaccine

Antigen/adjuvant vaccines. These vaccines are created by mass producing a few antigens from the tumor cell, altering them so they are more easily recognized by the patient's immune system, and injecting them into the patient. Sometimes an adjuvant, such as a weakened protein or bacteria, is added to the antigen to further stimulate the immune response.

Tumor cell vaccines. These vaccines are composed of cells from the patient's tumor that have been modified so they cannot reproduce. By injecting them into the patient, it is hoped they will stimulate the immune system to attack the specific antigen for that cancer and destroy original cancer cells that are replicating.

Dendritic cell vaccines. Dendritic cells are immune system cells that show antigens to T cells so they can produce antibodies. A dendritic cell vaccine trains the patient's dendritic cells to recognize the tumor antigen as foreign, then injects the "trained" dendritic cells into the patient so they can "train" T cells.

Idiotype vaccines. These vaccines are anti-tumor antibodies produced in the laboratory and injected into the patient where, it is hoped, they will attack cancer cell antigens.

DNA vaccines. DNA vaccines use genetic material from the tumor that encodes for one or more antigens to stimulate the immune response.

Vector-based vaccine. A vector-based cancer vaccine uses a virus, bacteria or yeast cell to "deliver" cancer antigens or DNA. The immune system responds to the vector as well as the cancer antigen, triggering a stronger immune response.

Autoimmune Vaccines

Therapeutic vaccines are also under investigation to treat autoimmune diseases like multiple sclerosis (MS) and lupus. These diseases result from an overactive immune system, one that fails to differentiate between "self" and "nonself" cells and attacks the body's own tissue.

Vaccines to treat such conditions are designed to "downregulate" the immune system by training certain immune cells to attack disease-causing immune cells. One such vaccine that has shown good results in early clinical trials is a DNA vaccine that targets the T cells that attack myelin, nerve cell sheathing, in people with MS.

Vaccines in the Future

Although we have made great strides in providing vaccines for many major illnesses, particularly childhood diseases, several other serious conditions remain. In addition to cancer vaccines researchers are working on vaccines to prevent malaria and HIV, the virus that causes AIDS. Vaccines are also being investigated to prevent hepatitis C, Alzheimer's disease, Parkinson's disease, myasthenia gravis and numerous other neurological and autoimmune diseases.

Malaria vaccine. Malaria is one of the most devastating diseases in the world, affecting more than 300 million people a year and killing more than 1 million, primarily in sub-Saharan Africa . The actual figures, however, are likely up to three times higher, given the difficulty of diagnosing and tracking the disease in these countries. Work on a vaccine, however, is finally paying off. A study published in late 2008 in the online edition of the New England Journal of Medicine showed the malaria vaccine protected 53 percent of the 402 people who received it. A slightly different formulation of the vaccine given to infants in the first four months of life in conjunction with other childhood vaccines showed an efficacy rate of 65 percent. Both give researchers hope that they may finally have a safe, relatively effective vaccine against malaria. The researchers concluded that the vaccine showed "promise" as a way of preventing transmission of the parasite responsible for the disease.

HIV vaccine. One of the most frustrating stories in the vaccine world has been the more than 20-year quest for a vaccine to prevent infection with the human immunodeficiency virus (HIV). That quest hit a new low in 2008 when plans for a large, government-sponsored clinical trial of a promising vaccine candidate were scrapped because it wasn't clear if the vaccine worked.

Then in November 2008, a report in the journal The Lancet announced what researchers already knew: Another good vaccine candidate, this one from Merck & Co., did not prevent HIV infection in the 3,000 people in whom it was tested. The vaccine used cold viruses to deliver bits of HIV. Results showed that uncircumcised men and those who showed the strongest response to the cold virus were more likely to become infected with HIV—not from the vaccine itself, but from some other, as yet unknown, process.

The challenge in developing a vaccine against HIV is that our immune system is woefully weak when it comes to eradicating the virus. The virus also takes over the DNA of normal immune system cells, often lying dormant for months or even years. When it is activated, it's too late for an immune response to be of use because the virus has co-opted cells to churn out millions of HIV copies. Another problem is that the virus mutates easily. A vaccine designed against today's virus would likely be irrelevant in a couple of years. Even when the immune system recognizes antigens on the virus and produces antibodies against it, the virus mutates before those antibodies can do much good. This is why existing drugs against the infection eventually fail; the virus mutates and becomes resistant to them.

Researchers aren't giving up, however. Instead, they are looking in new directions and thinking outside the conventional "vaccine box" to find unique approaches to tackling the challenge.

Facts to Know

Facts to Know

1. Today, more than 300 approved vaccines provide protection against 30 diseases.

2. The immune system has two components: the innate immune system, in which inflammation destroys invading pathogens; and the adaptive immune system, which "learns" to recognize certain pathogens and retains an immunologic memory so it can quickly mount a defense the next time the pathogen appears.

3. A vaccine is designed to stimulate the adaptive immune system before you're exposed to the virus or bacteria so you're already protected when you encounter it.

4. There are two main types of vaccine: prophylactic, which prevents disease; and therapeutic, which treats disease.

5. There are several types of vaccines, including live, attenuated vaccines and inactivated vaccines. The former are made with live, although weakened virus, while the latter is made with killed virus.

6. Adolescents and adults also require vaccination, including vaccines designed to protect against human papillomaviruses (HPV), which cause cervical cancer; influenza; pneumonia; and shingles. Adolescents and adults also require regular "booster" vaccines against diphtheria, tetanus and pertussis (whooping cough).

7. Prophylactic vaccines are extremely safe, although some may have mild side effects. The most common side effects are redness, soreness and irritation at the injection site and fever.

8. People with compromised immune systems, moderate-to-severe illnesses and/or those who have had a previous reaction to a vaccine should consult with their health care professional before getting vaccinated.

9. Researchers are working on vaccines that treat malaria, cancer, autoimmune diseases and neurological conditions like Alzheimer's disease and Parkinson's disease.

10. While many vaccines provide lifelong immunity, some require regular boosters.

Questions to Ask

Questions to Ask

Review the following "Questions to Ask" about vaccines so you are prepared to discuss this important health issue with your health care professional.

1. What are the possible side effects from this vaccine?

2. What are the potential implications if I don't vaccinate my child?

3. Is there anything I should do before having my child vaccinated to reduce the potential for side effects?

4. If my child misses one or more scheduled vaccines, can she catch up?

5. What vaccines does my 13-year-old need?

6. My 11-year-old daughter is not sexually active. Why does she need the HPV vaccine?

7. Can I participate in a clinical trial for a therapeutic vaccine to treat my cancer?

8. I'm worried about my child having several vaccines at one time. What are the advantages and disadvantages to vaccinating children this way?

9. I've heard that the MMR vaccine could cause autism. What does the research show?

10. Which type of flu vaccine should I have and why?

Key Q&A

Key Q&A

1. What is the difference between the innate and adaptive immune system?

   The innate immune system is designed to provide a kind of "shock and awe" protection against bacteria, viruses and other pathogens. When cells in the innate immune system "see" an invader, they rush in to destroy it, often by releasing inflammatory chemicals like histamines and leukotrienes. These invaders display "signs" on their surface called antigens that signal immune system cells to action.

   The adaptive immune system provides a more targeted approach. As immature T and B lymphocytes encounter antigens, they develop specific antibodies against those antigens. These "mature" lymphocytes hang out in tissue, ready to quickly spring to action when they encounter the same antigens. This creates immunologic memory and prevents reinfection.

2. How do vaccines work?

   All vaccines are designed to affect the immune system in some way. Prophylactic vaccines are designed to stimulate a response of the adaptive immune system to a modified version of the pathogen so that when you are infected with the actual virus or bacteria, it can quickly mount a major offense against the invader before you become sick. Therapeutic vaccines are designed to strengthen the immune system's response to a cancer or other abnormal cell.

3. What is the difference between live and "killed" vaccines?

   Live, attenuated vaccines contain a live, although significantly weakened, version of the virus or bacteria. Measles, mumps and chicken pox vaccines are made with live viruses. The benefit of a live vaccine is that a single dose often provides lifelong immunity. The downside is that because viruses and other pathogens naturally mutate, or change, the virus within the vaccine could also change, creating a more virulent version of itself that the immune system would have difficulty combatting. This was an issue with the early oral polio vaccines, but is generally not a problem with current live vaccines, which are much safer than the virus they protect against. Only people with a suppressed immune system (such as those who have HIV, are taking immunosuppressant drugs or are being treated for cancer) should be concerned about receiving live vaccines because they could, conceivably, become infected with the virus. These vaccines also usually require refrigeration.

   Inactivated vaccines contain a killed version of the pathogen. They are more stable (meaning they don't need refrigeration) and safer than attenuated viruses, but they don't elicit as strong an immune response. Thus, the immunity they provide may not last as long and you might need a "booster" vaccine down the road.

4. What types of vaccines protect against bacterial infections?

   Typically toxoid vaccines. Many bacteria secrete toxins that damage healthy cells. Toxoid vaccines treat the bacteria with formalin, which renders the toxins harmless but still retains enough of their structure to "teach" immune cells to recognize the bacteria and train them to lock onto the toxin antigen before the bacteria can release it. Toxoid vaccines are used for diphtheria and tetanus. Conjugate vaccines are also used in young children.

5. What should I do if my child misses a vaccine?

   Call your health care professional. Children can "catch up" on nearly all vaccines, regardless of their age.

6. What vaccines do adolescents require?

   Preteens and adolescents should receive vaccines against the human papillomavirus (girls only); meningococcal disease; whooping cough; influenza; hepatitis B; mumps/measles/rubella; polio; tetanus/diphtheria/acellular pertussis (Tdap); and varicella (chicken pox), depending on what vaccines they received when they were younger.

7. I'm traveling out of the country. What vaccines do I need?

   Make an appointment with your health care professional at least four to six weeks before your trip to see if you need any travel-related vaccines. The only required vaccines are yellow fever for those traveling to countries in sub-Saharan Africa and tropical South America and the meningococcal vaccine for travel to Saudi Arabia during the Hajj. You can learn more about vaccines required for overseas travel at the Centers for Disease Control Web site. Your local health department can typically provide the vaccines.

8. I'm worried about the safety of vaccines.

   Vaccines are extremely safe. The Centers for Disease Control and Prevention operates an Immunization Safety Office that continuously monitors vaccine safety, including side effects. Part of its mission is managing the vaccine adverse event reporting system, which serves as an "early warning" system to detect vaccine-related problems. About 30,000 reports are filed annually, but just 10 to 15 percent are classified as serious (causing disability, hospitalization, life-threatening illness or death). Anyone can file a report, including health care providers, manufacturers, personal injury lawyers and vaccine recipients or their parents or guardians.

9. I heard that vaccines can cause autism.

   Some parents insist that their children developed autism after having early childhood vaccines, such as the measles/mumps/rubella (MMR) vaccine. Some suspect that a preservative once used in childhood vaccines that contained mercury caused autism. But numerous scientific investigations regarding a possible link found no connection. Today's childhood vaccines do not have mercury-based preservatives; nonetheless, autism rates have continued to rise.

10. I have breast cancer. I heard there is a vaccine that can treat the cancer. How can I find out more?

    There are several vaccines under investigation for cancer. These are called therapeutic vaccines because they are designed to treat, rather than prevent, disease. However, none have been approved yet. So talk to your doctor about joining a clinical trial. You can find information about clinical trials for breast cancer vaccines at www.clinicaltrial.gov .

Organizations and Support

Organizations and Support

For information and support on Vaccines, please see the recommended Spanish-language resources listed below.

Centers for Disease Control and Prevention
Website: http://www.cdc.gov/spanish/inmunizacion/index.htm
Address: Centers for Disease Control and Prevention
1600 Clifton Road
Atlanta, GA 30333
Hotline: 1-800-232-4636