Effective control or total elimination of many childhood infections by vaccinations is one of the most remarkable success stories of modern mankind. Immunization is also among the most cost-effective preventive measures available. Currently, about 24 bacterial and viral pathogens are the targets of immunization with specific vaccines in the United States and other parts of the world. These vaccines include replicating or nonreplicating antigens delivered via systemic intramuscular, subcutaneous, or mucosal (intranasal, oral) routes as shown in Table 57.1. To benefit fully from immunization, susceptible subjects need to receive the recommended vaccines at the recommended ages. This helps ensure protection against the peak risks of the target diseases. Of the vaccines available currently, most have been employed for Universal Childhood Vaccination Programs in different parts of the world. The recommended immunization schedules with vaccines licensed for children and adolescents in the United States for the year 2009 (1) are shown in Tables 57.2 to 57.4. This chapter provides comprehensive information about each of the available vaccines. This information is designed to meet the needs of a first-time or occasional vaccine provider. However, other health care providers who immunize very frequently may obtain additional information from other sources, such as the published statements of the Advisory Committee on Immunization Practices (ACIP) of the US Public Health Service (available online at www.cdc.gov/vaccines/), the “Red Book” from the American Academy of Pediatrics, the frequently updated Bulletins of the World Health Organization, and the Morbidity and Mortality Weekly Report (MMWR) from the Centers for Disease Control and Prevention (CDC), Atlanta, GA.

The infection is caused by Bacillus anthracis, a spore-forming bacterium. It is a disease mainly of livestock. However, human infection may be acquired after exposure to infected animal products. The infection can be acquired through broken skin (cutaneous anthrax), by eating contaminated food (gastrointestinal anthrax), or by inhalation of anthrax spores (inhalation anthrax). Of the cases reported in the United States, 95% are cutaneous. The fatality rate for cutaneous anthrax is 5% to 20% without antibiotic treatment and less than 1% with antibiotic treatment. For those exposed through the digestive tract, the case fatality is estimated to be 25% to 60%. Before the availability of antibiotics or a vaccine, inhalation anthrax was almost always fatal. However, more recent experience suggests that early diagnosis and treatment significantly improves the prognosis and outcome.

The etiologic agent of diphtheria is Corynebacterium diphtheriae. The most common manifestation of diphtheria is severe pharyngitis. This is caused by a toxin released by the infecting organism that damages the respiratory epithelium, causing pseudomembrane formation. Toxin dissemination can also lead to nerve and cardiac muscle damage. Without treatment mortality is high particularly as a result of airway obstruction or cardiac dysfunction. Transmission occurs from person to person by close respiratory and physical contact.

Before vaccines were introduced in the late 1980s, Hib bacteria were the leading cause of purulent meningitis and epiglottis and an important cause of bacteremia, pneumonia, septic arthritis, and cellulitis in young children (5). About 1 child in 200 experienced invasive Hib infection by 5 years of age, half suffering from meningitis. The latter was the leading cause of acquired deafness and developmental delay. Hib organisms most often colonize the upper airway without causing disease and spread readily from child to child in respiratory secretions.

Immunity is associated with opsonic antibodies directed at the Hib capsular polysaccharide, polyribosyl ribose phosphate (PRP). Children do not respond to purified PRP until about 24 months of age, by which time about two-thirds of Hib cases have occurred. Response to PRP develops without T-cell help and lacks a memory component.

Hepatitis A virus (HAV) causes most cases of acute hepatitis in the United States (7). Young children are often mildly ill or asymptomatic but can readily spread infection to contacts. In older children, teens, and adults, HAV infection causes substantial morbidity for 1 to 3 months (2). Infection superimposed on chronic liver disease increases the risk of fulminant hepatitis or liver failure. No chronic infection state occurs. Infection spreads through the fecal route, through direct contact with cases, or through ingestion of contaminated food or water. Recovery is associated with lifelong protection.

Vaccination programs target individuals at high risk of infection and communities with high rates or recurrent epidemics of infection (8).

The hepatitis B virus (HBV) is a DNA virus which is an important cause of liver disease that ranges in severity from a mild illness lasting a few weeks (acute) to a serious long-term illness that can lead to chronic active hepatitis or liver cancer. This virus can be transmitted through contact with infectious blood, semen, and other body fluids from having sex with an infected person, sharing contaminated needles to inject drugs, or from an infected mother to her newborn (2).

The virus contains several important antigenic components. These include hepatitis B surface antigen (HBsAg), hepatitis B core antigen (HBcAg), and hepatitis B e antigen (HBeAg). Humans are the only known host for HBV, although some nonhuman primates have been infected in laboratory conditions. HBV is relatively resilient and, in some instances, has been shown to remain infectious on environmental surfaces for more than 7 days at room temperature. HBV infection is an established cause of acute and chronic hepatitis and cirrhosis. It is the cause of up to 80% of hepatocellular carcinomas and is second only to tobacco among known human carcinogens (2).

Human papillomaviruses (HPVs) are a group of more than 120 different virus types. Approximately 40 HPV types are primarily sexually transmitted from person to person (e.g., genital–genital contact, oral–genital contact, and sexual intercourse), infecting the oral, anal, or genital areas of both men and women. Genital HPV infections are very common: by 50 years of age, 70% to 80% of women and a similar percentage of men will have acquired genital HPV infection. Most genital HPV infections cause no symptoms and are cleared by the immune system within a few weeks or months.

Thus, the vast majority of people recover from genital HPV infection uneventfully. However, some people develop persistent or chronic genital HPV infection, which can lead to development of genital warts and anogenital cancers, especially cervical cancer.

Influenza virus infections affect more than 15% of children each winter, often in sharp, community-wide outbreaks. Infection causes substantial injury to the upper and lower respiratory tract, with high fever, conjunctivitis, coryza, sore throat, and prominent cough. Complications occur frequently and include otitis media, sinusitis, croup, bronchitis, and bronchopneumonia. Rarer complications include febrile convulsions, encephalopathy, and Reye syndrome. The infection spreads readily among school children and household members. Complications requiring medical care or hospitalization are more likely to occur in children younger than 2 years and in those of any age with debilitating lung or heart disease or other chronic conditions (18,19).

Immunization is recommended for children at increased risk of complications.

Japanese encephalitis (JE), a mosquito-borne arboviral (Flavivirus) infection, is the leading cause of viral encephalitis in Asia (2,21). Infection leads to overt encephalitis in 1 in 20 to 1,000 infected cases. Encephalitis usually is severe, resulting in a fatal outcome in 25% of cases and residual neuropsychiatric sequelae in 50% of cases. JE acquired during the first or second trimester of pregnancy may cause intrauterine infection and miscarriage. Infections that occur during the third trimester of pregnancy have not been associated with adverse outcomes in newborns. The virus is transmitted in an enzootic cycle among mosquitoes and vertebrate amplifying hosts, chiefly domestic pigs and, in some areas, wild Ardeid (wading) birds. Viral infection rates in mosquitoes range from less than 1% to 3%. These species are prolific in rural areas where their larvae breed in ground pools and flooded rice fields.
Thus, all elements of the transmission cycle are prevalent in rural areas of Asia and human infections occur principally in this setting. Because vertebrate amplifying hosts and agricultural activities may be situated within and at the periphery of cities, human cases occasionally are reported from urban locations.