Vaccination

Vaccination is the use of vaccines to prevent specific diseases.

Purpose

Many diseases that once caused widespread illness, disability, and death now can be prevented through the use of vaccines. Vaccines are medicines that contain weakened or dead bacteria or viruses. When a person takes a vaccine, his or her immune system responds by producing antibodies—substances that weaken or destroy disease-causing organisms. When the person is later exposed to live bacteria or viruses of the same kind that were in the vaccine, the antibodies prevent those organisms from making the person sick. Vaccines usually also stimulate the so-called cellular immune system as well. In other words, the person becomes immune to the disease the organisms normally cause. The process of building up immunity by taking a vaccine is called immunization.

Vaccines are used in several ways. Some, such as the rabies vaccine, are given only when a person is likely to have been exposed to the virus that causes the disease—through a dog bite, for example. Others are given to travelers planning to visit countries where certain diseases are common such as typhoid fever or yellow fever. Vaccines such as the influenza vaccine, or "flu shot," are given mainly to specific groups of people—older adults and others who are at high risk of developing influenza or its complications. Then, there are vaccines that are given to almost everyone, such as the ones that prevent diphtheria, tetanus, polio and measles.

Children routinely have a series of vaccinations that begins at birth. Given according to a specific schedule, these vaccinations protect against hepatitis B, diphtheria, tetanus, pertussis (whooping cough), measles, mumps, rubella (German measles), varicella (chickenpox), polio, pneumococcus and Haemophilus influenzae type b (Hib disease, a major cause of spinal meningitis) and, in some states, hepatitis A. This series of vaccinations is recommended by the American Academy of Family Physicians, the American Academy of Pediatrics, and the Centers for Disease Control and Prevention and is required in all states before children can enter school. All states will make exceptions for children who have medical conditions such as cancer that prevent them from having vaccinations, and some states also will make exceptions for children whose parents object for religious or other reasons.

Description

In addition to those discussed above, vaccines are available for preventing anthrax, cholera, hepatitis A, Japanese encephalitis, meningococcal meningitis, plague, pneumococcal infection (meningitis, pneumonia), tuberculosis, typhoid fever, and yellow fever. Most vaccines are given as injections, but a few are given by mouth.

Some vaccines are combined in one injection, such as the measles-mumps-rubella (MMR) or diphtheria-pertussis-tetanus (DPT) combinations.

Recommended dosage

The recommended dosage depends on the type of vaccine and may be different for different patients. The healthcare professional who gives the vaccine will decide on the proper dose.

A vaccination health record will help parents and health care providers keep track of a child's vaccinations. The record should be started when the child has his or her first vaccination and should be updated with each additional vaccination. While most physicians follow the recommended vaccination schedule, parents should understand that some flexibility is allowed. For example, vaccinations that are scheduled for age two months may be given anytime between six to 10 weeks. When possible,

An allergic reaction to a vaccination shot. (Photograph by Lester V. Bergman, Corbis Images. Reproduced by permission.)

follow the schedule. However, slight departures will not prevent the child from developing immunity, as long as all the vaccinations are given at around the right times. The child's physician is the best person to decide when each vaccination should be given.

Anyone planning a trip to another country should check to find out what vaccinations are needed. Some vaccinations must be given as much as 12 weeks before the trip, so getting this information early is important. Many major hospitals and medical centers have travel clinics that can provide this information. The Traveler's Health Section of the Centers for Disease Control and Prevention also has information on vaccination requirements.

Precautions

Vaccines are not always effective, and there is no way to predict whether a vaccine will "take" in any particular person. To be most effective, vaccination programs depend on whole communities participating. The more people who are vaccinated, the lower everyone's risk of being exposed to a disease. Even people who do not develop immunity through vaccination are safer when their friends, neighbors, children, and coworkers are immunized.

Like most medical procedures, vaccination has risks as well as substantial benefits. Anyone who takes a vaccine should make that sure he or she is fully informed about both the benefits and the risks. Any questions or

concerns should be discussed with a physician or other health care provider. The Centers for Disease Control and Prevention, located in Atlanta, Georgia, also is a good source of information.

Vaccines may cause problems for people with certain allergies. For example, people who are allergic to the antibiotics neomycin or polymyxin B should not take rubella vaccine, measles vaccine, mumps vaccine or the combined measles-mumps-rubella (MMR) vaccine. Anyone who has had a severe allergic reaction to baker's yeast should not take the hepatitis B vaccine. Patients who are allergic to antibiotics such as gentamicin sulfate, streptomycin sulfate or other aminoglycosides should check with their physicians before taking influenza vaccine, as some influenza vaccines contain small amounts of these drugs. Also, some vaccines, including those for influenza, measles and mumps, are grown in the fluids of chick embryos and should not be taken by people who are allergic to eggs. In general, anyone who has had an unusual reactions to a vaccine in the past should let his or her physician know before taking the same kind of vaccine again. The physician also should be told about any allergies to foods, medicines, preservatives, or other substances.

People with certain other medical conditions should be cautious about taking vaccines. Influenza vaccine, for example, may reactivate Guillain-Barré syndrome (GBS) in people who have had it before. This vaccine

How vaccines work: A.Vaccines contain antigens (weakened or dead viruses, bacteria, and fungi that cause disease and infection). When introduced into the body, the antigens stimulate the immune system response by instructing B cells to produce antibodies, with assistance from T-cells. B.The antibodies are produced to fight the weakened or dead viruses in the vaccine. C.The antibodies "practice" on the weakened viruses, preparing the immune system to destroy real and stronger viruses in the future. D.When new antigens enter the body, white blood cells called macrophages engulf them, process the information contained in the antigens, and send it to the T-cells so that an immune system response can be mobilized. (Illustration by Electronic Illustrators Group.)

also may worsen illnesses that involve the lungs, such as bronchitis or pneumonia. Vaccines that cause fever as a side effect may trigger seizures in people who have a history of seizures caused by fever.

Certain vaccines are not recommended for use during pregnancy, but some may be given to women at especially high risk of getting a specific disease such as polio. Vaccines also may be given to pregnant women to prevent medical problems in their babies. For example, vaccinating a pregnant woman with tetanus toxoid can prevent her baby from getting tetanus at birth.

Women should avoid becoming pregnant for three months after taking rubella vaccine, measles vaccine, mumps vaccine or the combined measles-mumps-rubella (MMR) as these vaccines could cause problems in the unborn baby.

Women who are breastfeeding should check with their physicians before taking any vaccine.

Side effects

Most side effects from vaccines are minor and easily treated. The most common are pain, redness, and swelling at the site of the injection. Some people may also develop a fever or a rash. In rare cases, vaccines may cause severe allergic reactions, swelling of the brain, or seizures. Anyone who has an unusual reaction after receiving a vaccine should get in touch with a physician right away.

Interactions

Vaccines may interact with other medicines and medical treatments. When this happens, the effects of the vaccine or the other medicine may change or the risk of side effects may be greater. For example, radiation therapy and cancer drugs may reduce the effectiveness of many vaccines or may increase the chance of side effects. Anyone who takes a vaccine should let the physician know all other medicines he or she is taking and should ask whether the possible interactions could interfere with the effects of the vaccine or the other medicines.