Routine vaccines across the life span, 2007

Journal of Family Practice, Feb, 2007 by Richard Kent Zimmerman, Donald B. Middleton, Ilene Timko Burns, Richard D. Clover, Sanford R. Kimmel

Routine vaccines are listed on the Recommended Childhood and Adolescent Immunization Schedule and the Recommended Adult Immunization Schedule published by the Centers for Disease Control and Prevention and reviewed and updated by the Advisory Committee on Immunization Practices. For these vaccines, we discuss the disease burden, rationale for vaccination, efficacy, adverse reactions, and recommendations. Some new vaccines are discussed here (Tdap and zoster), whereas others (rotavirus and human papillomavirus) are discussed elsewhere in the supplement.

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Routine vaccination has drastically reduced the burden of childhood diseases in the United States (TABLE 1). The significance of this effect is so great that immunizations are considered one of the major medical achievements of the 20th century.

The categories of indications for vaccination are age, underlying medical conditions, and high-risk occupation or lifestyle. Routine vaccines indicated by age are discussed in this article, including new recommendations (TABLE 2); high-risk indications are discussed in the next article. Important topics in deciding about routine use of vaccines include disease burden, rationale for vaccination, vaccine efficacy, adverse reactions, and official recommendations.

Hepatitis B Vaccine

Disease Burden

Since implementation of routine childhood immunization in the United States, an estimated 6800 perinatal and 18,700 nonperinatal infections among persons younger than age 10 have been prevented annually. (1) About 6000 persons die annually of hepatitis B virus (HBV)-related liver disease. Most of these deaths occur among persons with chronic HBV infection and are due to cirrhosis or primary hepatocellular carcinoma, which may affect adolescents and young adults. In fact, HBV infection is the second leading cause of cancer worldwide. Persons chronically infected with HBV in the United States, each of whom is potentially infectious, are estimated to number about 1.25 million, and the lifetime risk for acquiring HBV infection was estimated to be 5% before the introduction of hepatitis B vaccine. HBV infection clearly remains a major health problem in this country.

HBV infection is much more likely to become chronic when acquired early in life than when acquired during adulthood: chronic HBV infection develops in 90% of individuals infected in infancy, 30% of individuals infected before the age of 5 years, and less than 5% of individuals infected at age 5 years or olden. (2) Therefore, although most acute HBV infections in the United States occur during adulthood because of high-risk behaviors, 36% of all persons in the United States with chronic HBV infection contracted the infection during childhood. About 25% of individuals infected with HBV as infants will die of HBV-related chronic liver disease as adults, leading to a high number of years of potential life lost. (2)

HBV can be contracted by percutaneous or mucosal exposure to infectious fluids, namely blood, semen, or saliva. Transmission of HBV occurs primarily by blood exchange (eg, via shared needles during injection drug use) or by sexual contact. The source of infection is not identified for 30% to 40% of persons infected with HBV. (3) These cases may result from underreporting of injection drug use and sexual activity or inapparent contamination of skin lesions or mucosal surfaces (eg, hepatitis B surface antigen [HBsAg] has been found in saliva of persons chronically infected with HBV and on toothbrush racks and coffee cups in their homes). (4) Epidemiological studies show that HBV can be transmitted between preschool-age children. (5,6)

Rationale for Vaccination

Reasons to recommend routine infant vaccination against HBV infection include the following: (1) morbidity and mortality of HBV infection is substantial, especially when the virus is contracted during childhood when chronic infection is more likely, (2) prior strategies focusing on immunization of high-risk persons had little effect on incidence rates, and (3) many individuals who engage in high-risk behaviors (eg, injection drug use) become infected soon after beginning these behaviors.

The rationale for the birth dose includes missed opportunities for prophylaxis among infants born to mothers who are HBsAg positive that have resulted in chronic infection and its sequelae. In fact, only about half of expected births to HBsAg-positive women were identified for case management even though more than 95% of women are tested for HBsAg. (2) Thus, birth doses serve as a safety net to prevent perinatal infection.

The hepatitis B vaccines currently produced in the United States are manufactured by recombinant DNA technology using bakers yeast and do not contain human plasma. Pre-exposure vaccination results in protective antibody levels in almost all infants, children, and adolescents (>95%).

Duration of immunity. The duration of immunity in healthy persons is based on immunological memory; no clinical cases have been observed 15 to 20 years after vaccination in immunocompetent persons known to have responded to vaccination.: Although with time antibody levels may diminish after vaccination, most persons remain protected by immunologic memory in lymphocytes. The immunologic memory and long incubation period of HBV infection allow most immunized persons who have low titers to mount an anamnestic immune response if challenged by HBV. Rarely, a person who adequately responded to hepatitis B vaccine has developed asymptomatic HBV infection after exposure to the virus years after vaccination. However, no person so infected in the United States has become chronically infected or developed serious complications such as chronic liver disease. Of note, the duration of immunity in patients undergoing hemodialysis, in contrast to that of healthy persons, appears to persist only as long as the level of antibody to hepatitis B surface antigen (anti-HBs) is 10 mIU/mL or higher.