Vaccines

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.

In recent years, however, parents are increasingly likely to under-vaccinate their children. A January 2013 study published in JAMA Pediatrics reported that nearly half of children ages 2 months to 24 months in the United States either aren't getting all the necessary vaccines or have not been vaccinated at all. Vaccines are not just for kids. 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 typhoid. Preteen girls and boys can now be vaccinated against several strains of the human papillomavirus (HPV), which cause most cervical cancers, as well as cancer of the anus, vagina and vulva. 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 infected pus 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 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 may be 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. The only bacterial vaccine made with live pathogens in the United States is the typhoid vaccine.

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/AIDS, 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 not yet in use, though they are being tested for influenza and herpes. These vaccines are made of the organism's genetic material, which carries 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.

Recombinant vector vaccines. 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. 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, which then can provoke the immune response.

When to Vaccinate

These charts contain recommendations from the U.S. Centers for Disease Control and Prevention (CDC) 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" vaccinations 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.

Click on these charts to view the CDC recommendations:

• Children's vaccinations
• Teen vaccinations
• Adult vaccinations

The 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 percent and 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 20th century.

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, 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.

About 30,000 adverse event reports are filed annually, but just 10 percent to 15 percent are classified as serious (causing disability, hospitalization, life-threatening illness or death), and most 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 result 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 2 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 about 60 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 (and adults) definitely need vaccines and regular boosters. Children 11 or 12 need the tetanus-diphtheria-acellular pertussis (Tdap) vaccine; the meningococcal conjugate vaccine; the influenza vaccine; and the human papillomavirus (HPV) vaccine, which helps protect against cancers of the cervix, anus, vagina and vulva.

Plus, teens (and adults) who haven't had chicken pox or been immunized against the disease should get a varicella vaccine. Unfortunately, while vaccination rates for young children are very good, those for adolescents are far below what they should be, though some of these rates are improving.

According to the CDC, vaccination rates have been rising for tetanus-diphtheria (Tdap) and meningococcal-conjugate vaccine (MCV4). The increase in vaccine coverage rates for human papillomavirus (HPV) vaccine, however, is only about half the rate of the increases seen for Tdap and MCV4.

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 2010, nearly 28,000 cases were reported to the CDC. 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. Each year, an average of 60 people in the United States contract measles. But in 2011, the number of measles cases was higher than usual at 222. Most of these cases occurred in people who were not vaccinated, and 40 percent got measles in other countries and brought the disease back to the United States and spread it to others.

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

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.

There is currently one vaccine approved by the United States Food and Drug Administration to help treat cancer. The vaccine, called sipuleucel-t (Provenge), is a dendritic cell vaccine that treats advanced prostate cancer that no longer responds to hormone therapy. Researchers also have several cancer vaccines in late-stage clinical trials, including one to treat breast cancer. Click each type to learn more.

Antigen vaccines
Tumor cell vaccine
Dendritic cell vaccines
DNA vaccine
Vector-based vaccines

Antigen 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.

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.

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, tuberculosis, Alzheimer's disease, Parkinson's disease 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. Scientists at the CDC have an ongoing malaria vaccine development and evaluation program that is testing potential malaria vaccines in small New World monkeys.

HIV vaccine. Researchers throughout the world have been working on an HIV vaccine for more than 20 years without success. In the United States alone, the National Institute of Allergy and Infectious Diseases at the National Institutes of Health has conducted more than 117 HIV vaccine clinical trials to test more than 70 possible vaccines. The U.S. Military HIV Research Program and the CDC are also researching HIV vaccines.

The challenge in developing a vaccine against HIV is that our immune system is 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 may 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.

However, scientists still believe a vaccine to prevent HIV is possible, and they are building on what they have learned and moving forward with the research process.

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 pathogens, while the latter are made with killed pathogens, or parts of them.

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

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 teenage child need?

6. My preteen 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