David Slotnick, M.D.
Vaccination is one of the best ways to protect the body against disease. When someone is vaccinated, elements of a disease that has been weakened or inactivated are injected into the body. This stimulates the immune system to fight the invading disease. After the immune system has overcome the disease, it creates cells that stay alert for the disease-causing microbes, making the body immune to that particular disease.
In some cases, immunity lasts for life. However, some vaccines require a booster shot some time later.
Different types of vaccines are used to protect against different diseases. Types of vaccine include:
- Live vaccine. Contains live versions of a virus or bacterium that have been weakened to not cause disease in the body. This produces a strong immune reaction and in many cases protects for life.
- Inactivated vaccine. Contains a dead version of the virus or bacterium. Inactivated vaccines may not produce a strong immune reaction and booster shots are sometimes required.
- Subunit vaccine. Contains only the antigens of the disease-causing microbe, which reduces the risk of the body reacting adversely to the vaccine.
- Toxoid vaccine. Contains the toxins that are sometimes secreted by bacteria. A toxoid vaccine only protects against diseases caused by certain toxins.
- Conjugate vaccine. Designed for infants and young children. A conjugate vaccine protects infants and young children from microbes that may take advantage of their immature immune systems.
In addition to these types of vaccinations, scientists are experimenting with vaccines that contain the DNA of diseases. These vaccines may be able to protect people against diseases for which there are currently no vaccines available, such as HIV and malaria.
Most vaccinations are given during early childhood. Vaccines are most effective when they are given at the earliest point that the immune system can respond effectively to a disease-causing microbe. Additionally, children are also more vulnerable to many diseases than adults. Childhood vaccination is one of the ways that diseases such as measles, which used to be one of the most common and deadly diseases among children in the United States, have been essentially eradicated.
People who travel to other countries may need vaccinations to protect them against diseases that are uncommon in the United States. Diseases that travelers are commonly vaccinated against include yellow fever, typhoid fever and hepatitis A. Scientists are constantly researching new methods of vaccination that can improve immunity throughout the world. There is also considerable research involved in providing vaccines for diseases such as HIV and possible agents of bioterrorism.
Vaccination is a method of immunization whereby elements of a disease are injected (or sprayed) into the body to stimulate the immune system to react. Usually, once the immune system has fought the vaccine, the body becomes resistant to the particular microbes that cause the disease. Vaccination is one of the most effective ways to prevent disease in individuals and eradicate diseases from communities.
A vaccine usually includes a weakened or dead microbe. When the microbe enters the body, antigens from the microbe alert the immune system to the presence of a foreign body. Antigens also tell the immune system what type of microbe is present. This allows the body to release antibodies that can fight the disease-causing microbes. After a period of time, the antibodies destroy the microbe and stimulate the creation of cells that will remain alert to that particular microbe. If the microbe is encountered again, the immune system will be able to fight it quickly before it causes disease in the body.
There are vaccines for many different diseases. Some must be administered during childhood and can protect people throughout their lives. Others can be administered later in life if a person is likely to encounter a particular disease (e.g., when people travel to a foreign country). Certain vaccines can be administered after infection. This is the case for rabies, measles, hepatitis B and tetanus because of the long incubation periods for these diseases.
Some vaccines may produce side effects that vary in severity from mild swelling or itching at the injection site to a more serious allergic reaction. However, most side effects of vaccines are mild and easily treatable.
In recent years, there has been speculation about a potential link between childhood vaccinations and an increase in the incidence of certain conditions, including autism and attention deficit hyperactivity disorder (ADHD). The speculation has centered on the number of recommended childhood vaccines, which has increased, and the use of preservatives such as thimerosal (a compound containing mercury) in some vaccines. However, numerous studies have addressed these issues and have found no evidence of links in either case. Thimerosal has been removed or reduced to trace amounts in all childhood vaccines except for the inactivated influenza vaccine as a precaution against unnecessary toxic exposure. According to the U.S. Food and Drug Administration, there is no convincing evidence of harm caused by the small amounts of thimerosal contained in influenza vaccines – other than minor symptoms of swelling or redness at the site of injection.
Many diseases that used to be common in the United States are no longer a threat because of rigorous vaccination campaigns. This has made some people reluctant about vaccinating themselves or their children because they think that the risk of side effects is more urgent than the chances of contracting the disease. However, the majority of side effects from vaccinations are mild, and there are rarely complications associated with vaccines. Measles has been essentially eradicated through vaccines in the United States, but isolated cases still occur among people who have not been vaccinated.
Smallpox has been eliminated worldwide through rigorous vaccination programs. The virus no longer exists naturally and only remains in controlled laboratory conditions. The general public no longer receives smallpox vaccines and has not for more than 30 years. Recently, concern has arisen that smallpox could be spread through bioterrorism. If terrorists acquired the virus, it could spread quickly in an unvaccinated population. However, the U.S. government still maintains large supplies of smallpox vaccine to fight such a threat.
Some common vaccinations include:
- Hepatitis B vaccine (HBV). Protects against hepatitis B, which infects the liver and can lead to long-term problems such as cirrhosis or cancer of the liver. The vaccine is given in three separate injections during childhood.
- Diphtheria, tetanus and pertussis vaccine (DTaP). Protects against diphtheria (serious throat infection), tetanus (serious nerve disease) and pertussis (respiratory illness sometimes known as “whooping cough”). DTaP is provided in a series of five injections from ages 2 months to 6 years. After the final dosage has been administered, tetanus and diphtheria booster shots are urged every 10 years. Diphtheria has been eradicated and tetanus has been nearly eradicated in the United States as a result of this vaccine. The vaccine is up to 80 percent effective in preventing pertussis infections.
- Hib vaccine. Immunizes patients against haemophilus influenzae type b bacteria, which was the leading cause of meningitis in children prior to the development of this vaccine. It is given in three doses and a booster from 2 months to 15 months. More than 90 percent of infants who receive at least three doses of the vaccine are protected against meningitis, pneumonia, inflammation of the membrane covering the heart (pericarditis), and certain infections of the blood, bones and joints.
- Inactivated polio vaccine (IPV). Prevents polio, a virus that can cause permanent paralysis. The vaccine is typically administered four times between ages 2 months and 6 years. More than 95 percent of children who are vaccinated will be protected against polio, which has been eradicated in the United States as a result this vaccine. Previously, children often received this vaccine in oral form. Today, it is given almost exclusively by injection, which eliminates the small risk of developing polio that was associated with the live oral vaccine.
- Pneumococcal conjugate vaccine (PCV). Protects against pneumococcal infections, which can lead to pneumonia, blood infections and bacterial meningitis. This infection is spread through direct contact with another person and is most dangerous to children under 2. Immunizations are given through four injections between ages 2 months and 15 months, and they provide three years of protection. PCV is also given to children who have sickle cell anemia, a damaged spleen, HIV/AIDS and diseases (e.g., diabetes, cancer) and medicines (e.g., steroids, chemotherapy) that affect the immune system.
- Measles, mumps and rubella vaccine (MMR). Protects against measles, mumps and rubella (also known as German measles). The vaccine is given in two doses between the ages of 12 months and 6 years. More than 95 percent of children who receive the vaccine will be protected from these diseases. Adults with certain conditions such as diabetes, heart, kidney or liver disease (other than cancer) or HIV should also receive the MMR vaccine if they did not do so as a child.
- Chickenpox (varicella) vaccine. Protects against chickenpox, a common childhood illness. The vaccine is typically given once, although older children may require two doses given one month apart. The vaccine prevents severe forms of chickenpox in 95 percent of those who are immunized, and prevents milder forms in 85 percent of those who are immunized.
- Influenza vaccine (flu shot). Protects against influenza (flu), one of the most common preventable infectious diseases in children and adults. It can be given as an injection or a nasal spray, although the nasal spray vaccine is not approved for children under 5 years, pregnant women or people with conditions that may weaken their immune system. The flu vaccine needs to be administered yearly because of the propensity of the flu virus to mutate over short periods of time and become resistant to previously used vaccines. While there has been some debate over the actual effectiveness of the influenza vaccine, studies show substantial benefit. Experts typically recommend this vaccine for children, older adults, and people with weakened immune systems.
Some vaccines, such as the vaccine for hepatitis A, offer protection for life. However, vaccines such as tetanus and diphtheria require booster shots. A booster shot is an additional dose of the vaccine that is given either once or regularly (for example, every 10 years). It stimulates the immune system again and ensures that the body is adequately protected. People should discuss any allergies they may have with their physician before being vaccinated. Some vaccines (including the vaccines for measles, mumps, influenza and yellow fever) use substances that are derived from eggs, which can be dangerous for people who are allergic to eggs. Additionally, some vaccines may include traces of antibiotics that may cause a reaction in people who are allergic to the specific type of antibiotics used.
Types and differences of vaccinations
Different diseases require different types of vaccines. Types of vaccines include:
- Live vaccine. Also known as attenuated (weakened) vaccine because it contains live versions of a virus or bacterium that have been weakened so as not to cause disease in the body.
A live vaccine produces a very strong immune system response and often protects people for life. However, there is a small possibility that the weakened microbe introduced through the vaccine could mutate into a disease-causing microbe. For this reason, live vaccines are unsuitable for people with impaired immune systems, such as people with HIV/AIDS or cancer. Examples of diseases that can be prevented by a live vaccine include:
- Yellow fever
Inactivated vaccines are safer and more stable than live vaccines because there is no chance that the dead microbe will mutate into a disease-causing microbe. This makes inactivated vaccines more suitable for people with weakened immune systems. Examples of diseases that can be prevented by an inactivated vaccine include:
The conjugate vaccine combines toxins and antigens that the child’s immune system will recognize (along with the associated sugar molecules) in order to produce an immune system response. The child’s immune system can then respond to the sugar molecules present on the disease-causing microbes. Examples of diseases that can be prevented by a conjugate vaccine include:
- Haemophilus influenzae type b (Hib) disease
- Streptococcal pneumonia
These types of vaccines have the potential to be effective in preventing illnesses such as HIV and malaria because they generate a strong antibody response without the risk of using a live microbe. They are also cheap and easy to produce. Scientists are still experimenting with DNA vaccines and, currently, there are no DNA vaccines approved by the Food and Drug Administration (FDA) for use in humans.
- Recombinant vector vaccines. These vaccines are still being researched, although they appear to have the potential to prevent many types of illnesses. Recombinant vector vaccines are similar to DNA vaccines, except that they use a harmless microbe shell (known as the vector, or vehicle of transmission) to introduce the genetic material from a disease-causing microbe to the human body. Thus, a harmless microbe mimics a harmful microbe, producing a strong immune system response. A weakened microbe may also be used as the vector in this type of vaccine.
Most vaccinations are given in childhood. Many diseases are most common in early childhood and the immune systems of young children are still developing and may need an extra boost. Most states require that children receive certain vaccinations before they are allowed to attend daycare, school or camp.
Vaccination schedules are compiled by the Advisory Committee on Immunization Practices (ACIP), which advises the U.S. Centers for Disease Control and Prevention (CDC) and U.S. Department of Health and Human Services. Vaccination schedules reflect both the time that a person is first able to react to an antigen and the time when people are most likely to contract the disease. This is usually during early childhood, although there are some vaccinations that may need to be given again later in life.
A schedule of some standard childhood vaccinations is as follows:
|Hepatitis B||First dose: Birth to 2 months Second dose: 1-4 months Third dose: 6-18 months11-12 years (if necessary)|
|Diphtheria, tetanus, pertussis (DTaP)||First dose: 2 months Second dose: 4 months Third dose: 6 months Fourth dose: 15 months Fifth dose: 4-6 yearsBooster shot: 11 – 12 years (tetanus and diphtheria)|
|Haemophilus influenza type b (Hib)||First dose: 2 months Second dose: 4 months Third dose: 6 monthsFourth dose: 12-15 months|
|First dose: 2 months Second dose: 4 months Third dose: 6-18 monthsFourth dose: 4-6 years|
|Pneumococcal(PCV7)||First dose: 2 months Second dose: 4 months Third dose: 6 monthsBooster: 12-15 months|
|First dose: 12-15 months Second dose: 4–6 years11-12 years (if not received earlier)|
|Chickenpox (varicella)||First dose: 12-18 months 11-12 years (if not received earlier)|
Vaccinations that may also need to be administered later in life include:
- Influenza. Each year, influenza is believed to infect between 5 percent and 20 percent of the American population, making it one of the most common infectious diseases in the United States. It can largely be prevented by getting the flu shot in October or November, before the beginning of flu season, which can last from October to May.
The CDC recommends that people at high risk for the flu, including people over age 50 and those with chronic illnesses, receive a flu shot each year. The composition of the flu shot changes every year because the virus mutates easily and can become resistant to previous vaccines, making annual vaccination necessary for continued protection.
In addition, the American Academy of Pediatrics, American Academy of Family Physicians and the CDC’s Advisory Committee for Immunization Practice (ACIP) all recommend that children between the ages of 6 months and 23 months begin receiving an annual influenza vaccine. Children with chronic medical conditions (e.g., asthma, cystic fibrosis, diabetes) and children on long-term aspirin therapy for certain conditions (e.g., Kawasaki disease) should also receive the influenza vaccine each year. Some studies show that this vaccine can reduce the risk of getting the flu by up to 80 percent during flu season.
- Pertussis (whooping cough). There has been a recent upsurge in the number of cases of whooping cough after it was thought to be all but eliminated in the United States. It is believed that this may be due to the vaccine wearing off by early adulthood. As a result, college campuses and nursing homes have become fertile ground for outbreaks of whooping cough, which is then spread to infants who are not yet fully immunized. The ACIP recommends that all people over the age of 11 receive a booster shot of the pertussis vaccine.
- Diphtheria, tetanus. A booster shot is required every 10 years for life to maintain immunity against these diseases. Adults who are not current on their diphtheria or tetanus vaccinations or who did not receive their initial series of shots during childhood should receive these vaccinations every 10 years.
- Pneumococcus. Adults over 65 or those with long-term health problems, especially conditions that weaken the immune system, should receive this vaccination. According to the CDC, pneumococcus is one of the most common causes of death in the United States from a vaccine-preventable disease. Older adults may be particularly susceptible to life-threatening complications due to this disease.
- Measles, mumps and rubella (MMR). Measles, mumps and rubella are serious diseases in children and adults. The CDC recommends that people born after 1957 (when the diseases were more prevalent and natural immunity was common) who have not already received the MMR vaccine should be vaccinated. It is especially important for women of childbearing age to receive the vaccine because rubella can cause miscarriage and birth defects.
- Chickenpox (varicella). Although children are more likely to contract the chickenpox virus than adults, the disease is more serious in adults. Chickenpox in adults may lead to shingles, which can damage the eyes or other organs. Adults with chickenpox are also more likely to develop pneumonia. Before the introduction of the vaccine in 1995, approximately 50 adults died each year from chickenpox. Adults who do not remember receiving the vaccine or experiencing the disease should consult with their physician about whether they should be vaccinated.
- Meningococcal vaccine. In recent years there have been several cases of meningitis outbreaks in schools and colleges. This is thought to be a result of living in close proximity to other people (such as in a dorm room) at an age where immunity from childhood vaccination (usually given at age 11 or 12) may be waning. The American College Health Association now recommends that adolescents receive a meningococcal vaccination before they start college.
- Human papilloma virus (HPV). In 2006, the U.S. Food and Drug Administration (FDA) approved a vaccine to protect against several strains of HPV, a common sexually transmitted infection that may cause genital warts in men and women and can infect the cervix in women. Left untreated, HPV in women may lead to cervical cancer.
The vaccine is most effective when given before the onset of sexual activity, when a person has not been exposed to HPV. After the vaccine’s approval, the ACIP recommended that the HPV vaccine be routinely given to 11- and 12-year-old girls. The vaccine is approved for use in girls and women ages 9 to 26. It is given in a series of three shots over a six-month period.
International travel and vaccination
When people travel outside their home country, they often come into contact with various microbes that their immune system may not have encountered before. This increases the risk of contracting a serious disease. There are vaccines available for many diseases found outside the United States, so it is important that people consult their physician before traveling to determine what vaccines may be necessary.
Further information on vaccines that may be required before traveling to certain countries can be found by contacting the World Health Organization (WHO) or the U.S. Centers for Disease Control and Prevention (CDC).
Some common vaccines that people who travel may require include:
- Hepatitis A. Hepatitis A (HAV) is prevalent in many countries and is spread through contact with the feces of an infected person. In places with poor sanitation, it is commonly transmitted by contaminated food and water or by infected food service workers. People who are planning to travel to areas with high rates of HAV (e.g., Africa, Central and South America, Asia, Middle East, Russia) should consult their physician about the need for HAV vaccination.
- Yellow fever. Yellow fever is spread by mosquitoes and can be found in Africa and South America. It can cause flu-like symptoms and, in some cases, severe hepatitis and hemorrhagic fever. According to the CDC, the disease is fatal in more than 20 percent of cases of infection. Travelers can protect themselves from yellow fever by receiving the live-virus yellow fever vaccine, which provides immunity for up to 10 years.
- Typhoid fever. Typhoid fever is caused by the bacterium Salmonella typhi. In developing countries, it affects roughly 12.5 million people each year and is a particular threat for travelers to Asia, Africa, and Central and South America. Like hepatitis A, it is spread by contact with the feces of an infected person and can be carried on food or in water. It is easily vaccinated against, although booster shots are needed every two to five years to maintain immunity.
- Polio. Although the polio vaccine provides lifetime immunity, some physicians recommend a polio booster for people traveling to areas where polio is endemic.
- Rabies. Rabies can be found on nearly every continent. It is mostly commonly spread by bites from infected animals, although in rare instances it can be transmitted through other kinds of contact with infected animals. People who are traveling to areas with high rates of rabies or who may be handling or otherwise having contact with animals are advised to have a rabies vaccination. The rabies vaccination will not stop rabies from being transmitted if a person is bitten. However, it will substantially slow down the progression of the virus and allow medical aid to be given before the disease becomes serious.
In the United States, most pets are required to be vaccinated against rabies. This limits the spread of this disease should a pet bite a human. However, a rabies vaccination may be necessary for anyone who is bitten by an animal with an unknown vaccination history.
There is currently no vaccine available for malaria, which is one of the most common infectious diseases worldwide. People traveling to a country with high malaria rates should consult their physician about ways they can reduce their risk of infection. This may include taking anti-malarial medication both before and after travel and protecting themselves from mosquito bites. While they are not available yet, researchers are investigating potential malaria vaccines.
Ongoing research regarding vaccinations
Researchers are constantly working to develop new vaccines and improve old vaccines. One of the chief motivating factors is reducing the rate of illness in the developing world. The use of live vaccines, which are among the most effective for many diseases, is often impractical in places where refrigeration is not possible. The production of inexpensive and practical vaccines for use in developing countries is key to eliminating many of the diseases that are prevalent in those parts of the world. Scientists are working on various vaccine alternatives, including:
- Edible vaccines. Scientists are in the process of developing a type of vaccine that can be administered by eating genetically engineered fruit and vegetables. For example, potatoes have been genetically engineered to produce a response against E. coli antigens and bananas are being developed to protect against Norwalk virus, which is a common cause of diarrhea.
- Skin patch vaccines. Vaccines that could be administered through a skin patch are currently being tested in both laboratory mice and humans. Antibody response to the bacteria E. coli, for example, has been observed in humans who used a skin patch vaccine.
- Nasal spray vaccines. A nasal spray to replace the flu vaccine was recently approved by the Food and Drug Administration for use in people aged 5 to 49 who are not pregnant. This live vaccine is thought to be more effective than the traditional flu shot because it replicates the way in which the flu virus enters the body – through the respiratory system – therefore producing a better immune response. It is thought that this method of vaccination could be used for other diseases.
In addition to new vaccination methods, scientists are constantly testing vaccines for new diseases. Some of the most important vaccine research is being directed toward finding a vaccine for HIV. Trials for the HIV vaccine started in 1988 but scientists have yet to produce a suitable vaccine. Additionally, researchers are also attempting to create vaccines that could protect against possible agents of a bioterrorism attack.
Questions for your doctor about vaccination
Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to vaccinations:
- Where can I find a vaccination schedule for myself and my children?
- Are there any diseases that I should be vaccinated against?
- Are there any alternatives to needle-stick vaccinations?
- Is there a risk I may get sick from my vaccination?
- Could I be allergic to any parts of the vaccine?
- What are the possible side effects from this vaccination?
- Will I need a booster shot?
- When should I get a booster shot?
- What vaccinations should I have before traveling?
- Should I get vaccinated before I get pregnant?
- Will the vaccination interfere with my pregnancy?