Hepatitis A in U.S. Drops Substantially After Vaccination Implementation

Following implementation of an expanded program of hepatitis A vaccination of children, the overall hepatitis A rate in the U.S. has declined by 76 percent, according to a study in the July 13 issue of JAMA.

 

In the United States, an average of 26,000 hepatitis A cases were reported annually to public health agencies during the 1980s and 1990s, representing an estimated 270,000 infections per year when anicteric disease and asymptomatic infections are taken into account, according to background information in the article. More than half of the estimated infections occurred among children. In 1995, highly effective hepatitis A vaccines became available in the United States for use among persons aged 2 years or older, providing an opportunity to substantially reduce hepatitis A incidence. In 1996, the Advisory Committee on Immunization Practices recommended targeted hepatitis A vaccination of selected high-risk populations and routine vaccination for children living in communities with the highest hepatitis A rates. In 1999, this committee expanded its recommendations for routine vaccination of children to include children living in 17 states that had consistently elevated hepatitis A rates and a distinctive pattern of hepatitis A epidemiology.

 

Annemarie Wasley, ScD, of the Centers for Disease Control and Prevention (CDC), and colleagues analyzed data from a national hepatitis A surveillance to determine changes in the incidence and epidemiology of hepatitis A in the United States since 1990 and following implementation of recommendations for hepatitis A vaccination.

 

The researchers found that between the baseline period (1990-1997) and 2003, overall hepatitis A rates declined 76 percent to 2.6 per 100,000, significantly lower than previous lows in 1983 (9.2/100,000) and 1992 (9.1/100,000). The rate of hepatitis A in vaccinating states declined 88 percent to 2.5 per 100,000 compared with 53 percent elsewhere (to 2.7/100,000). In 2003, cases from vaccinating states accounted for 33 percent of the national total vs. 65 percent during baseline period. Declines were greater among children aged 2 to 18 years (87 percent) than among persons older than age 18 years (69 percent); the proportion of cases in children dropped from 35 percent to 19 percent. Since 2001, rates in adults have been higher than among children, with the highest rates now among men aged 25 through 39 years.

 

In summary, we report early apparent impact of implementation of a novel, and to our knowledge, unique vaccination strategy. This strategy is based on distinctive features of hepatitis A epidemiology, including the geographic clustering of areas with consistently elevated rates, the important role of children in sustaining transmission, and the hypothesized large effect of herd immunity. These features lent themselves to a geographically focused strategy using a vaccine that could not be readily integrated into the routine vaccination schedule, and maximized the impact of limited vaccination. The changes we describe represent a transformation in hepatitis A epidemiology in the United States. However, because hepatitis A incidence has historically exhibited a pattern of periodic increases, further monitoring is needed to determine the extent to which the declines that have occurred will be sustained and are attributable to vaccination. In addition, more data on vaccine coverage levels are needed to better describe the relationship between hepatitis A vaccine usage and disease rates, the authors write.

 

Sustaining and further reducing hepatitis A incidence can be achieved by improving vaccination coverage in groups for which it is currently recommended, including children living in the historically higher-rate states and children and adults in high-risk groups. Elimination of hepatitis A virus transmission will require expansion of existing recommendations to include routine vaccination of all U.S. children, the researchers conclude.

 

Reference: JAMA. 2005;294:194201

 

Source: American Medical Association

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