CHAPTER 173
Immunization
Immunization enables the body to better defend itself against diseases caused by certain bacteria or viruses. Immunization may occur on its own (when people are exposed to bacteria or viruses), or doctors may provide it. When people are immunized against a disease, they do not get the disease or get only a mild form of it.
There are two types of immunization: active and passive.
In active immunization, vaccines are used to stimulate the body’s natural defense mechanisms. Vaccines are preparations that contain one of the following:
Noninfectious fragments of bacteria or viruses
A usually harmful substance (toxin) that is produced by a bacteria but has been modified to be harmless—called a toxoid
Weakened (attenuated), live whole organisms that do not cause infection
The body’s immune system responds to a vaccine by producing substances (such as antibodies and white blood cells) that recognize and attack the specific bacteria or virus contained in the vaccine. Then whenever the person is exposed to the specific bacteria or virus, the body automatically produces these antibodies and other substances. The process of giving a vaccine is called vaccination, although many doctors use the more general term immunization.
In passive immunization, antibodies against a specific infectious organism are given directly to a person. These antibodies are obtained from several sources:
The blood (serum) of animals (usually horses) that have been exposed to a particular organism or toxin and have developed immunity
Blood collected from a large group of people—called pooled human immune globulin
People known to have antibodies to a particular disease (that is, people who have been immunized or who are recovering from the disease)—called hyperimmune globulin—because these people have higher levels of antibodies in their blood
Antibody-producing cells (usually taken from mice) grown in a laboratory
Passive immunization is used for people whose immune system does not respond adequately to an infection or for people who acquire an infection before they can be vaccinated (for example, after exposure to the rabies virus). Passive immunization can also be used to prevent disease when people are likely to be exposed and do not have time to get or complete a vaccination series. For example, a solution containing gamma globulin (a common type of antibody) is used to help prevent hepatitis in people who travel to certain parts of the world. Passive immunization lasts for only a few days or weeks, until the body eliminates the injected antibodies.
Did You Know…
Some vaccines contain a weakened but living form of the virus that they protect against.
Vaccines and antibodies are usually given by injection into a muscle (intramuscularly) or under the skin (subcutaneously). Antibodies are sometimes injected into a vein (intravenously).
Vaccines available today are highly reliable, and most people tolerate them well. They rarely have side effects, but they do not work in everyone.
Some vaccines are given routinely—for example, the tetanus toxoid is given to adults, preferably every 10 years. Some vaccines are routinely given to children.
Other vaccines are usually given mainly to specific groups of people. For example, the yellow fever vaccine is given only to people traveling to certain parts of Africa and South America. Still other vaccines are given after possible exposure to a specific disease. For example, the rabies vaccine may be given to a person who has been bitten by a dog.
Common Vaccinations
Children typically are given a number of vaccines according to a standard schedule (see art on page 1685). If vaccines are missed, most can be given later, according to a catch-up schedule. Adults may also be advised to receive certain vaccines. When advising adults about vaccination, a doctor considers the person’s age, health history, childhood vaccinations, occupation, geographic location, travel plans, and other factors. Because vaccines are widely used in the United States, many diseases, once common, are now rare or well controlled.
More than one vaccine may be given at a time. They may be given in one combination vaccine or in individual injections at different injection sites.
Vaccines usually cause no problems, although mild side effects, such as soreness or redness at the injection site, may occur. There has been concern about the safety of thimerosal (a mercury-based preservative in some vaccines) in infants, but there is no evidence of harm. In particular, there is no convincing evidence that vaccines containing thimerosal are related to the development of autism. Nevertheless, most manufacturers have developed thimerosal-free vaccines for use in infants. Information about vaccines that currently contain low levels of mercury or thimerosal is available at the Institute for Vaccine Safety web site.
The only reason for not being vaccinated is a serious allergic reaction (such as an anaphylactic reaction) to the vaccine or to one of its components. However, some vaccines, usually ones that contain live virus, should not be used or should be delayed in people with certain conditions:
A weakened immune system due to a disorder, such as AIDS, or to drugs that suppress the immune system (immunosuppressants), including corticosteroids
Pregnancy
Some progressive nervous system disorders, such as Guillain-Barré syndrome
Diphtheria-Tetanus-Pertussis
The diphtheria, tetanus, and pertussis vaccine is a combination vaccine that protects against these three diseases:
Diphtheria usually causes inflammation of the throat and mucous membranes of the mouth. However, the bacteria that cause diphtheria produce a toxin that can damage the heart, kidneys, and nervous system. Diphtheria was once a leading cause of death in children.
Tetanus causes severe muscle spasms, which result from a toxin produced by bacteria. The bacteria usually enter the body through a wound.
Pertussis (whooping cough) is a very contagious respiratory infection that is particularly dangerous to children younger than 2 years old and to people who have a weakened immune system.
PROTECTING CHILDREN THROUGH VACCINES
| DISEASE | WHEN DO VACCINATIONS TYPICALLY START |
| Chickenpox (varicella) | Age 12-15 months |
| Diphtheria | Age 2 months |
| Haemophilus influenzae type b infections (such as meningitis) | Age 2 months |
| Hepatitis A | Age 12-18 months |
| Hepatitis B | Birth |
| Human papillomavirus (for girls) | Age 11 years |
| Influenza | Age 6 months |
| Measles | Age 12-15 months |
| Meningococcal meningitis | Age 11-12 years Age 2 years for children at high risk |
| Mumps | Age 12-15 months |
| Pertussis | Age 2 months |
| Pneumococcal infections | Age 2 months |
| Polio | Age 2 months |
| Rotavirus | Age 2 months |
| Rubella (German measles) | Age 12-15 months |
| Tetanus | Age 2 months |
The vaccine has two forms: DTaP for children under 7 years and Tdap for adolescents and adults. Tdap has lower doses of diphtheria and pertussis vaccine, indicated by the lower case d and p.
Administration: The vaccine is given as an injection into a muscle. Five injections are given: typically at age 2 months, 4 months, 6 months, 15 to 18 months, and 4 to 6 years. Because pertussis is becoming more common among adults, a booster is recommended at age 11 to 12 years to be followed by a tetanus-diphtheria booster every 10 years. Adults who missed the series of vaccinations given during childhood should get it as adults.
PROTECTING ADULTS THROUGH VACCINES
| DISEASE* | WHO SHOULD BE VACCINATED |
| Anthrax | People who may be exposed to anthrax, such as the following:
|
| Chickenpox (varicella) | All adults who have not had the vaccine or the disease |
| Diphtheria | All adults (usually as a combination vaccine with tetanus and pertussis) |
| Haemophilus influenzae type b infections (such as meningitis) | Adults at increased risk, such as the following:
|
| Hepatitis A | Adults at increased risk, such as the following:
|
| Hepatitis B | Adults at increased risk, such as the following:
|
| Human papillomavirus | All females aged 11-26 years |
| Influenza | Adults over 50 Anyone who requests vaccination, particularly those at increased risk, such as the following:
|
| Measles | All adults who have not had the infection or two doses of the vaccine, usually given as a combination vaccine with mumps and rubella |
| Meningococcal meningitis | People at increased risk, such as the following:
|
| Mumps | All adults who have not had the infection or two doses of the vaccine, usually given as a combination vaccine with measles and rubella |
| Pertussis (whooping cough) | All adults (usually given as a combination vaccine with tetanus and diphtheria) |
| Pneumococcal infections (such as meningitis and pneumonia) | Adults at increased risk, such as the following:
|
| Polio | Adults at increased risk, such as travelers to areas where polio is common |
| Rabies | People who have been bitten by certain animals |
| Rubella (German measles) | All adults who have not had the infection or two doses of the vaccine, usually given as a combination vaccine with measles and mumps |
| Shingles (herpes zoster) | People over 60 |
| Smallpox | Not currently recommended except for military personnel |
| Tetanus | All adults (boosters every 10 years after the primary series, which is usually given during childhood as a combination vaccine with diphtheria and tetanus) |
| Tuberculosis (bacille Calmette-Guérin, or BCG) | Not usually used in the United States |
| Typhoid | People traveling to areas where the disease is common |
| Yellow fever | People traveling to certain parts of Africa and South America, where the disease is common |
| * Vaccines are available In the United States for these diseases. | |
Side Effects: The injection site may become sore, swollen, and red. Serious side effects are rare. They include high fever, inconsolable crying, seizures, and a severe allergic reaction. Serious side effects usually result from the pertussis part of the vaccine. If they occur, the pertussis vaccine is not used again. A vaccine against diphtheria and tetanus may be used instead to complete the vaccination series. The vaccine is not repeated if seizures occur 3 to 7 days after the vaccine is given.
Haemophilus influenzae Type b
The Haemophilus influenzae type b (Hib) vaccine helps protect against bacterial infections due to Hib, such as pneumonia and meningitis. These infections may be serious in children. Use of the vaccine has decreased the incidence of serious infections in children by 99%. These infections are uncommon in adults.
Different formulations of the vaccine are available.
Administration: The vaccine is given as an injection into a muscle. Doses are given at age 2 months and 4 months or at age 2 months, 4 months, and 6 months, depending on which formulation is used. In either case, a final dose is given at age 12 to 15 months (for a total of three or four doses). All children should be vaccinated. Adults at increased risk of these infections (such as those with a weakened immune system) may benefit from this vaccination.
Side Effects: Occasionally, the injection site becomes sore, swollen, and red.
Hepatitis A
The hepatitis A vaccine helps protect against hepatitis A. Typically, hepatitis A is less serious than hepatitis B. Hepatitis A often causes no symptoms, although it can cause fever, nausea, vomiting, and jaundice. Hepatitis A does not lead to chronic hepatitis. Use of the vaccine has reduced the number of people who become infected.
Administration: The hepatitis A vaccine is given as an injection into a muscle. Two doses are given to all children: typically at age 12 to 18 months and 6 to 12 months later. It is also recommended for adults at increased risk of the infection.
Side Effects: Sometimes the injection site is sore. No serious side effects have been reported.
Hepatitis B
The hepatitis B vaccine helps protect against hepatitis B. Generally, hepatitis B is more serious than hepatitis A and is occasionally fatal. Symptoms can be mild or severe. They include decreased appetite, nausea, and fatigue. In 5 to 10% of people, hepatitis B becomes chronic.
Administration: The vaccine is typically given in a series of three injections into a muscle. However, if people who have been vaccinated are exposed to the virus, a doctor measures their antibody levels against hepatitis B. If the antibody levels are low, they may need another injection of hepatitis B vaccine.
Vaccination is recommended for all children and adults, especially for adults at high risk of exposure to the hepatitis B virus.
Side Effects: Occasionally, the injection site becomes sore, and a mild fever develops. People with a history of severe allergic reaction to baker’s yeast, which is used in the production of the vaccine, should not be given the vaccine.
Herpes Zoster
The herpes zoster vaccine helps reduce the risk of shingles (herpes zoster) and the residual pain it can cause (postherpetic neuralgia). The herpes zoster virus is the same virus that causes chickenpox. After chickenpox resolves, the virus remains in the body. It can be reactivated years later and cause shingles, which is a painful rash, usually on only one part of the body. The rash resolves after several weeks, but postherpetic neuralgia can last for months or years.
The vaccine is similar to the varicella vaccine and contains live virus.
Administration: The vaccine is given in one dose as an injection under the skin. It can be given to people over 60.
Side Effects: Rarely, the injection site becomes sore.
Human Papillomavirus
The human papillomavirus (HPV) vaccine helps protect against cervical cancer and genital warts, which are caused by the human papillomavirus.
Administration: The vaccine is given as an injection into a muscle in three doses: initially, then at 2 and 6 months after the first dose. It is recommended for girls aged 11 to 13 years but can be given up to age 26.
Side Effects: The injection site sometimes becomes sore, swollen, and red. No serious side effects have been reported.
Influenza
The influenza virus vaccine helps protect against influenza. There are two types of influenza virus, type A and type B, and many different strains within each type. The strains of virus that cause influenza outbreaks change each year. Thus, a new vaccine is needed each year.
Influenza can be mild, causing fever, aches, and fatigue, but it can be serious, sometimes causing death—usually in children under age 1 year or in people over 65.
Administration: The vaccine is given as a single injection into the muscle. The vaccine is recommended for children aged 6 to 59 months, people over 50, and others who are at increased risk. Also, the vaccine is usually given to anyone who requests it.
Influenza vaccine is available as an injection or a nasal spray. The nasal spray, which contains live virus, is recommended only for healthy people who are aged 2 to 49 and not pregnant.
Influenza epidemics usually begin in late December or midwinter. Therefore, the best time to get the vaccine is in September or October. A vaccine against avian influenza has been developed in case the virus becomes able to spread from person to person.
Did You Know…
People with an egg allergy may have an allergic reaction to the influenza vaccine because it is made from viruses grown in eggs.
Side Effects: Occasionally, the injection site becomes sore. Very rarely, the vaccine causes Guillain-Barré syndrome, a progressive nerve disorder. The nasal spray sometimes causes a runny nose and sore throat. People who have a severe allergy to eggs may have a severe allergic reaction to the vaccine because the vaccine is made from viruses grown in eggs.
Measles, Mumps, and Rubella
The measles, mumps, and rubella (MMR) vaccine is a combination vaccine that helps protect against these three viral infections:
Measles causes a rash, fever, and cough. It affects mainly children. In healthy children, it is rarely serious. However, it can lead to brain damage or pneumonia and is occasionally fatal.
Mumps causes the salivary glands to swell and become painful. Mumps can affect the testes, brain, and pancreas, especially in adults. Mumps is more serious in adults.
Rubella (German measles) causes a runny nose, swollen lymph nodes, and a rash with a light reddening of the skin, especially the face. In adults, it may cause joint pain. If pregnant women get rubella, they may miscarry, the fetus may die, or the baby may have birth defects.
Administration: The vaccine is given as an injection under the skin. Two doses are given: at age 12 to 15 months and typically at age 4 to 6 years. If people born after 1956 have never had any one of these infections and have not received two doses of the vaccine, they should be given at least one dose of the vaccine. Adults who are likely to be exposed to these diseases (such as those beginning college, joining the military, working in schools or child care centers, or traveling internationally) should get a second dose of the vaccine.
Pregnant women and people who are have had serious allergic reactions to gelatin or to the antibiotic neomycin should not be vaccinated.
There are individual vaccines for measles, mumps, or rubella. However, a combination vaccine that helps protect against all three is usually used. The combination vaccine is recommended because anyone who needs protection against one of these infections usually also needs protection against the other two.
Side Effects: Some people have mild side effects, such as a fever, a general feeling of illness (malaise), and a rash. Joints may become temporarily stiff and painful, usually in teenage girls and women.
Meningococcal Infections
The meningococcal vaccine protects against infections caused by the bacteria, Neisseria meningitidis, which can lead to meningitis or death. These bacteria are the leading cause of bacterial meningitis in children and the second leading cause of bacterial meningitis in adults. The infection can cause the following symptoms:
Initially, fever, nausea, headache, and leg pain
Later, a rash, decreased blood pressure, and cold hands and feet
Progression from feeling well to being very sick within hours
Administration: The vaccine is given in one dose as an injection under the skin or into a muscle. Two formulations are available in the United States: the polysaccharide vaccine for children aged 2 to 10 years and the conjugate vaccine for people aged 11 years or older.
The meningococcal vaccine is recommended for all children at age 11 to 12 years. It is also recommended for the following:
Children aged 2 to 10 years if they have a weakened immune system, sickle cell disease, or a chronic infection
Adolescents entering high school if they have not already been vaccinated
All college students living in dormitories and military recruits if they have not already been vaccinated
Travelers to areas where the disease is common
Adults who do not have a functioning spleen
Side Effects: The injection site may become sore, swollen, and red. A few people have a mild fever and fatigue. Guillain-Barré syndrome developed in a few people after they were vaccinated with the conjugate vaccine. Thus, this vaccine should not be given to people who have had this syndrome.
Pneumococcal Infection
Pneumococcal vaccines help protect against bacterial infections caused by Streptococcus pneumoniae, such as ear infections, sinusitis, pneumonia, and meningitis.
Administration: Two formulations of the pneumococcal vaccine are available. The conjugate vaccine is given typically at age 2 months, 4 months, 6 months, and 12 to 15 months. The polysaccharide vaccine is given to older children at high risk of developing pneumonia or another pneumococcal infection in two doses: at age 24 months and 3 to 5 years later. The polysaccharide vaccine is also recommended for older children and adults who are at high risk of developing these infections.
The polysaccharide vaccine is effective in about two of three adults, although it is less effective in debilitated older people. It is more effective in preventing some of the serious complications of pneumococcal pneumonia than in preventing the pneumonia itself. Although one injection of the vaccine may provide lifetime protection, people at high risk are advised to be vaccinated again after 5 years.
Side Effects: Occasionally, the injection site becomes painful and red. Other side effects include fever, irritability, drowsiness, loss of appetite, and vomiting.
Polio
The polio vaccine protects against polio, a very contagious viral infection that affects the nerves. Polio can cause permanent muscle weakness, paralysis, and sometimes death.
Smallpox: A Vaccine in the Wings
The smallpox vaccine has not been routinely given in the United States for 30 years because the disease has been eliminated. Because the vaccine’s protective effects wear off after about 10 years, most people are now susceptible to smallpox.
Recent fears about the possible use of smallpox by terrorists have led to the suggestion that smallpox vaccination resume. If smallpox vaccination is resumed, it is likely to be recommended only for people in the area of a smallpox outbreak. Military personnel are now vaccinated, and enough smallpox vaccine has been prepared to vaccinate everyone in the United States if needed.
The vaccine is generally safe, although serious adverse effects occur in about 100 of every million previously unvaccinated people, and death occurs in 1 per million. The risk of serious adverse effects and death is lower in previously vaccinated people.
The vaccine is most effective when given very early after exposure. However, the vaccine may also be beneficial if given in the first days after symptoms appear. There is no treatment for smallpox.
Two formulations are available. One contains killed virus and is injected. The other contains live, weakened virus and is taken by mouth. The live-virus vaccine is no longer available in the United States because it causes polio in about 1 of every 2.4 million people who receive the vaccine.
Administration: The vaccine is given in four doses: at age 2 months, 4 months, 6 to 18 months, and 4 to 6 years. Because polio is now so rare in the United States, unvaccinated people over 18 years are not given the vaccine unless they are traveling to an area where polio is common.
Side Effects: People who have allergies to the antibiotics streptomycin, neomycin, or polymyxin B may have an allergic reaction to the vaccine. The vaccine may contain small amounts of these antibiotics.
Rotavirus
The rotavirus vaccine helps protect against gastroenteritis, which causes vomiting, diarrhea, and, if symptoms persist, dehydration.
Administration: This vaccine is part of the recommended vaccination schedule for children. Three doses are given: at age 2 months, 4 months, and 6 months.
Side Effects: No severe side effects have been reported, but mild, temporary diarrhea occurs in 1 to 3% of children within 7 days of receiving the vaccine.
Tetanus
The tetanus vaccine protects against the toxin produced by the tetanus bacteria, not the bacteria itself. Typically, the bacteria enter the body through a wound and begin to grow and produce the toxin. The toxin causes severe muscle spasms and can be fatal. Therefore, vaccination is particularly important.
Administration: The vaccine is typically given during childhood, as part of the diphtheria, tetanus, and pertussis vaccine (see page 1145). The combination vaccine is given in five injections, followed by a booster that contains the same amount of tetanus vaccine but a smaller amount of diphtheria and pertussis vaccine. The booster is given at age 11 to 12 years. Because immunity against pertussis is decreasing, people aged 16 to 64 should receive this booster if they have not received it previously. A booster of the tetanus vaccine is recommended every 10 years thereafter. Also, people sometimes need to be vaccinated after an injury.
Side Effects: Sometimes the injection site is sore, swollen, and red. Serious side effects are rare and include severe allergic reactions.
Varicella
The varicella vaccine helps protect against chicken-pox (varicella), a very contagious infection caused by the varicella-zoster virus. It causes an itchy rash that looks like small blisters with a red base. In some people, the brain, lungs, heart, and joints become infected. The virus remains in the body. If it is reactivated, it can cause shingles years later.
Administration: Vaccination against varicella is part of the routine vaccination schedule recommended for children. The vaccine is given as an injection under the skin. Two doses are given: at age 12 to 15 months and at age 4 to 6 years. It is also recommended for all adolescents and adults who have not had the vaccine or the disease. It is given to them in two doses 4 to 8 weeks apart.
Because the vaccine contains live virus, it is not given to pregnant women, people with a weakened immune system, or people with cancer of the bone marrow or lymphatic system.
Side Effects: The vaccine is safe, and side effects are mild. In fewer than one fourth of the people who get the vaccine, the injection site becomes painful, swollen, and red. Very occasionally, a chickenpox-like rash develops.
Taking aspirin and related drugs (salicylates) after vaccination can cause Reye’s syndrome in children under 16 years old. Thus, such children should not be given these drugs for 6 weeks after vaccination.
Vaccination Before Foreign Travel
Residents of the United States may be required to receive specific vaccines before traveling to areas that have infectious diseases not normally found in the United States (see table on page 2101). Recommendations change frequently in response to disease outbreaks. The Centers for Disease Control and Prevention (CDC) provide the most up-to-date information on vaccination requirements in their Travelers’ Health section.