Public health impact of immunization

Widespread vaccination has had a profound impact on public health. In the United States, vaccination has greatly reduced the incidence of some infectious diseases (eg, pertussis, mumps, tetanus) and virtually eliminated five others: diphtheria, smallpox, poliomyelitis, rubella, and measles (Table 68–1). With two diseases, results have been even more dramatic: wild-type polio is gone from the Western hemisphere, and smallpox is gone from the planet.

Despite these successes, we still have a long way to go: Although our national vaccination rate is at an all-time high, every year 2.1 million children ages 1 to 3 years receive few or no vaccinations. In some parts of the country, more than 50% of the children are not current. The consequences of failing to vaccinate can be enormous. For example, between 1989 and 1991, a measles epidemic occurred; 55,000 cases were reported, 11,000 people were hospitalized, and more than 130 people died, half of them young children.

The Childhood Immunization Initiative, begun in 1993, is directed at preventing such epidemics in the future. The goal is to eliminate all indigenous cases of diphtheria, measles, rubella, tetanus, and H. influenzae type b infection from the United States. The program aims to achieve these goals by improving vaccine delivery systems, increasing community participation, reducing vaccine costs to parents, developing safer and simpler vaccines, and involving more federal agencies in providing vaccines to populations who otherwise might not have access to them. Thanks to these strategies, three of these diseases—diphtheria, rubella, and measles—are virtually gone from this country.

From a strictly economic viewpoint, vaccination is a sound investment. On average, we save $14 in future healthcare costs for every dollar we spend on vaccination.

Reporting vaccine-preventable diseases

Public health officials rely on healthcare providers to report cases of VPDs. Nearly all VPDs that occur in the United States are notifiable. Healthcare providers should report individual cases to their local or state health department. Each week, the state health departments make a report to the Centers for Disease Control and Prevention (CDC). The information is used to (1) determine if an outbreak is occurring, (2) evaluate prevention and control strategies, and (3) evaluate the impact of national immunization policies and practices.

Immunization records

The National Childhood Vaccine Act of 1986 requires a permanent record of each mandated vaccination a child receives. The information should be recorded in either (1) the permanent medical record of the recipient or (2) a permanent office log or file. The following data are required:

The purpose of these records is twofold. First, they help ensure that children receive appropriate vaccinations. Second, they help avoid overvaccination, and thereby reduce the risk of possible hypersensitivity reactions. To promote uniformity in record keeping, an official immunization card has been adopted by every state and the District of Columbia.

Adverse effects of immunization

Vaccines are generally very safe. Although mild reactions are common, serious events are rare. Many children experience local reactions (discomfort, swelling, and erythema at the injection site). Fever is also common. Very rare but severe effects include anaphylaxis (eg, in response to measles, mumps, and rubella virus vaccine [MMR]); acute encephalopathy (caused by diphtheria and tetanus toxoids and pertussis vaccine [DTP]); and vaccine-associated paralytic poliomyelitis (VAPP) (caused by oral poliovirus vaccine [OPV]). In 2011, the safety of vaccines was reaffirmed in a lengthy report—Adverse Effects of Vaccines: Evidence and Causality—issued by the Institute of Medicine of the National Academies.

Vaccinations can hurt. This pain, in turn, can lead to needle fears, procedural anxiety, and avoiding additional immunizations. Accordingly, minimizing pain is a primary goal. Strategies to reduce pain and anxiety include holding the child upright during the vaccination, applying a topical anesthetic, providing tactile stimulation, performing IM injections rapidly without prior aspiration, and injecting the most painful vaccine last. Pain can be further reduced by use of microneedles, needle-free devices, and intranasal vaccines. What about giving analgesic/antipyretics, such as acetaminophen and ibuprofen? Recent evidence indicates that giving these drugs before or shortly after vaccination can reduce the immune response. Accordingly, routine use of these drugs to prevent pain and/or fever should be discouraged.

Immunocompromised children are at special risk from live vaccines. The reason is that, in the absence of an adequate immune response, the viruses or bacteria in these normally safe vaccines are able to multiply in profusion, thereby causing serious infection. Accordingly, live vaccines should generally be avoided in children who are severely immunosuppressed. Causes of immunosuppression include congenital immunodeficiency, HIV infection, leukemia, lymphoma, generalized malignancy, and therapy with radiation, cytotoxic anticancer drugs, and high-dose glucocorticoids.

Some parents are concerned that thimerosal, a mercury-based preservative found in some vaccines, might cause autism. For two reasons, this concern is unfounded. First, several large, high-quality studies conducted in Denmark, Britain, and the United States have failed to show a causal link between childhood immunization using thimerosal-containing vaccines and development of autism. Second, thimerosal is being phased out of vaccines made here (owing to concerns about mercury exposure, not concerns about autism). At this time, the amount of thimerosal in most routinely used childhood vaccines is either zero or extremely low (less than 0.5 mcg per 0.5-mL dose). The only exceptions are certain flu vaccines, which still contain thimerosal as a preservative. However, even if these flu vaccines are used, total mercury exposure from childhood vaccination will still be well below the limit considered safe by the Food and Drug Administration (FDA) and the Environmental Protection Agency.

The risk of serious adverse reactions can be minimized by observing appropriate precautions and contraindications. Table 68–2 lists contraindications that apply to all vaccines. Precautions and contraindications that apply to specific vaccines are discussed in the context of those preparations. Certain conditions, such as diarrhea and mild illness, may be inappropriately regarded as contraindications by some practitioners. As a result, vaccination may be needlessly postponed. Conditions that are often considered contraindications, although they are not, are also listed in Table 68–2.

Practitioners are required to report certain adverse events to the Vaccine Adverse Event Reporting System (VAERS). The information is used to help determine whether (1) a particular event that occurs after vaccination is actually caused by the vaccine, and (2) what the risk factors might be. In addition to reporting events that they are required to report, practitioners should report all other serious or unusual adverse events, regardless of whether they believe the event was caused by the vaccine. Forms for reporting adverse events can be obtained from the VAERS web site (www.vaers.hhs.gov) or by calling 1-800-822-7967.

The National Vaccine Injury Compensation Program (NVICP), established by the National Childhood Vaccine Injury Act of 1986, was created to provide compensation for injury or death resulting from vaccination. The program is intended as an alternative to civil litigation in that negligence need not be proved. As a provision of the law, a table was created listing the vaccines covered by the program and the injuries, disabilities, illness, and conditions—including death—for which compensation may be paid. Compensation may also be paid for injuries not listed in the table, provided that (1) a listed vaccine is involved and (2) causality can be demonstrated. Injuries related to vaccines not listed in the table are not covered under the program. Additional information can be obtained by calling the NVICP automated recording at 1-800-338-2382.

Vaccine information statements

The National Childhood Vaccine Injury Act requires that Vaccine Information Statements (VISs) be given to all vaccinees (or their parents or legal representatives) before certain vaccines are administered. The VISs, produced by the CDC, are one-page, two-sided documents that describe the benefits and risks of specific vaccines. For vaccines that require a series of shots, a VIS must be given before each dose, not just the first dose. The VISs are available in over 30 languages, and can be obtained online at www.cdc.gov/vaccines/pubs/vis/default.htm.

Childhood immunization schedule

Each year, the CDC’s Advisory Committee on Immunization Practices (ACIP), in cooperation with the American Academy of Family Physicians and the American Academy of Pediatrics, issues revised recommendations for childhood immunization in the United States. Figures 68–1 and 68–2 (see pp. 871–872) show the recommended schedule for 2011. You can find the catch-up immunization schedule for persons ages 4 months through 18 years and the most recent updates online at www.cdc.gov/vaccines/.

Measles, mumps, and rubella

Diphtheria, tetanus, and pertussis

Poliomyelitis

Poliomyelitis, also known as polio or infantile paralysis, is a serious disease in which the poliovirus attacks neurons of the central nervous system that control muscle movement. The result is skeletal muscle paralysis, usually in the legs. However, muscles of respiration and muscles of the arms may be affected too. In about 10% of cases, polio is fatal. The disease is caused by three different polioviruses. Paralytic polio is usually caused by type 1 poliovirus. Polio has no cure. However, proper symptomatic treatment can improve comfort and reduce or prevent some crippling effects. Vaccination against polio has eliminated the disease from the Western hemisphere, except for eight to nine cases annually caused by the vaccine itself. To prevent vaccine-induced polio, use of the live virus vaccine (oral polio vaccine) has been discontinued in the United States. The number of cases worldwide was 1315 in 2007—nearly double the 784 cases documented in 2003.

Haemophilus influenzae type b

Haemophilus influenzae type b is a gram-negative bacterium that can cause meningitis, pneumonia, and serious throat and ear infections. The bacterium is the leading cause of serious illness in children under the age of 5 years, and the most common cause of bacterial meningitis, which has a mortality rate of 5%. Among children who survive meningitis, between 25% and 35% suffer lasting neurologic deficits. As a result of childhood vaccination, the annual incidence of infection dropped from an estimated 20,000 cases in 1984 to less than 208 in 2008. Of the cases that occurred, almost all were in unvaccinated children. Infection with H. influenzae can be treated successfully with antibiotics.

Varicella (chickenpox)

Varicella (chickenpox) is a common, highly contagious, and potentially serious disease of childhood. The causative organism is varicella-zoster virus, a member of the herpesvirus group. Patients typically develop 250 to 500 maculopapular or vesicular lesions, usually on the face, scalp, or trunk. Other symptoms include fever, malaise, and loss of appetite. Among children, the most common complications are bacterial suprainfection and acute cerebellar ataxia. Reye’s syndrome and encephalitis develop rarely. Among adults, the most serious common complication is varicella pneumonia. As a rule, symptoms in adults are more severe than in children: Hospitalization is 10 times more likely in adults, and death is 20 times more likely. Although adults account for only 2% of varicella cases, they account for 50% of varicella-related deaths. Before varicella vaccine became available, over 90% of children in the United States got chickenpox by age 11, which corresponds to 4 million cases a year. In addition, about 11,000 victims were hospitalized each year, and about 100 died. Since universal vaccination began in 1995, hospitalizations have dropped dramatically: One study indicates that, between 2000 and 2006, an estimated 50,000 hospitalizations were avoided.

Herpes zoster, also known as shingles or simply zoster, develops in 15% of patients years after childhood chickenpox has resolved. The cause is reactivation of varicella-zoster viruses that had been dormant within sensory nerve roots. Episodes of zoster begin with neurologic pain in the area of skin supplied by the affected nerve roots. Blister-like lesions develop within 3 to 4 days, and usually disappear 2 to 3 weeks later. However, in about 14% of patients, neurologic pain persists for a month or more—and in a few cases, pain lasts for years.

Hepatitis B

Hepatitis B is a serious liver infection caused by the hepatitis B virus. Acute infection can cause anorexia, malaise, diarrhea, vomiting, jaundice, pain (in muscles, joints, and stomach), and death. Chronic infection can result in cirrhosis, liver cancer, and death. Each year in the United States, hepatitis B infects 50,000 people, puts 11,000 in the hospital, and kills 3000 to 5000. Worldwide, 170 million people have chronic hepatitis B, and 250,000 die from it annually.

Although hepatitis B is found in virtually all body fluids, only blood, serum-derived fluids, saliva, semen, and vaginal fluids are infectious. The most common modes of transmission are needle-stick accidents, sexual contact with an infected partner, maternal-child transmission during birth, and use of contaminated IV equipment or solutions.

Hepatitis B is discussed further in Chapter 93 (Antiviral Agents I: Drugs for Non-HIV Viral Infections).

Hepatitis A

Hepatitis A is a serious liver infection caused by the hepatitis A virus. In the United States, hepatitis A infects between 125,000 and 200,000 people annually, and causes about 100 deaths (from acute liver failure). Symptoms of hepatitis A include fever, malaise, nausea, jaundice, anorexia, diarrhea, and stomach pain. However, not all infected persons become symptomatic. Among children less than 6 years old, only 30% develop symptoms. In contrast, symptoms are present in most older infected children and adults. When symptoms do occur, they develop rapidly and then usually fade in less than 2 months. However, between 10% and 15% of patients experience prolonged or relapsing disease that persists up to 6 months. During the course of the infection, the virus undergoes replication in the liver, passage into the bile, and then excretion in the feces. As a result, the usual mode of transmission is fecal-oral in the context of close personal contact with an infected person. In addition, hepatitis A can be contracted by ingesting contaminated food or water. Blood-borne transmission is rare. Individuals at risk include household and sexual contacts of infected individuals, international travelers, and people living in areas where hepatitis A is endemic (eg, American Indian reservations, Alaskan Native villages).

Pneumococcal infection

In the United States, Streptococcus pneumoniae (pneumococcus) is the leading bacterial cause of childhood meningitis, sepsis, pneumonia, and otitis media. Among children with pneumococcal meningitis, up to 50% suffer permanent brain damage or hearing loss, and about 10% die. The risk of acquiring pneumococcal infection is highest for children under the age of 2 years. Factors that increase infection risk include sickle cell disease, immunodeficiency, asplenia, chronic diseases, attending a group day care center, and being a Native American, African American, Alaskan Native, or socially disadvantaged person. Worldwide, pneumococcal infection ranks among the leading causes of death from infectious disease. Routine childhood immunization against pneumococcal disease began in 2000. Since then, the incidence of severe pediatric infection has dropped sharply.

Meningococcal infection

Meningococcal infection is a serious disease caused by Neisseria meningitidis, also known as the meningococcus. Invasive meningococcal disease is a leading cause of meningitis in American children. Worldwide, the majority of infections are caused by five N. meningitidis serogroups—designated A, B, C, Y, and W-135—identified on the basis of antigenic differences in surface polysaccharides. In the United States, only three serogroups—B, C, and Y—cause most cases. Meningococcal infection is readily transmitted through direct contact with respiratory secretions from patients and from asymptomatic carriers. Injury results from a meningococcal endotoxin, which is produced so quickly that death can result within hours of infection onset. Although only 1400 to 2800 cases occur here each year, the disease is clearly of great concern, with a fatality rate of 10% to 14% despite antibiotic therapy. Furthermore, of those who survive, 11% to 19% suffer severe and permanent sequelae, including neurologic disability, deafness, mental retardation, and limb amputations. Infection rate is highest during infancy, with a second peak during adolescence and early adulthood. Outbreaks can occur in day care centers, schools, and colleges. Risk factors for acquiring the disease include immunodeficiency, antecedent viral infection, household crowding, chronic underlying disease, active and passive smoking, and anatomic and functional asplenia. A meningococcal vaccine was approved in 1981, but it was not very effective in children. Hence, routine childhood immunization was not recommended until 2005, the year a more effective vaccine was introduced.

Influenza

Influenza is a serious infection of the respiratory tract and a major cause of morbidity and mortality worldwide. Characteristics of the influenza virus and of influenza itself (mode of transmission, symptoms, time course, methods of prevention and treatment) are discussed in Chapter 93.

Rotavirus gastroenteritis

Rotavirus, which infects the intestinal mucosa, is the most common diarrheal pathogen worldwide. Infection presents initially as upset stomach and vomiting, usually with fever, and then progresses to several days of diarrhea, which can be mild to severe. The combination of vomiting and severe diarrhea can result in life-threatening dehydration. Virtually all children become infected repeatedly within the first 5 years of life. However, the first episode is generally the worst. As a result, severe diarrhea and dehydration are most likely in the very young—children 3 to 35 months old. Before a rotavirus vaccine became available, rotavirus infected 2.7 million American children under the age of 5 each year, resulting in more than 400,000 office visits, 55,000 to 70,000 hospitalizations, and 20 to 60 deaths. Worldwide, annual deaths are estimated in the hundreds of thousands. Infected children shed large amounts of rotavirus in their stool, and hence transmission is usually fecal-oral, resulting from touching the stool or a contaminated object. Rotavirus infection can be prevented with two vaccines: RotaTeq and Rotarix. An older vaccine—RotaShield—was withdrawn owing to a high rate of intussusception, a life-threatening blockage of the intestine.