Decline of Hepatitis A in the US: Another Vaccine Success Story

Abstract

Source: Wasley A, Samandari T, Bell BP. Incidence of hepatitis A in the United States in the era of vaccination. JAMA. 2005;294:194–201.In the 1980s and 1990s, an average of 26,000 cases of hepatitis A was reported annually in the United States, with an estimated 270,000 infections per year when anicteric and asymptomatic cases were included.1 More than half of the infections occurred in children. In 1995, hepatitis A vaccine became available in the US. In 1999, routine vaccination was recommended for children living in 11 states with the highest incidence of hepatitis; vaccination was suggested for children living in 6 additional states with above-average rates of hepatitis A.2Fundamental changes in the epidemiology of hepatitis A were detected in an analysis of national hepatitis A surveillance data by the Viral Hepatitis Division of the Centers for Disease Control and Prevention in Atlanta (CDC). Incidence rates of hepatitis A in 2003 were compared with those for the prevaccination baseline period (1990 to 1997) overall and in the 17 states in which vaccination is either recommended routinely or suggested. Incidence rates in vaccinating states also were compared to rates in states with no recommendations for routine vaccination. Between the baseline period (1990 to 1997) and 2003, overall hepatitis A rates declined 76% to 2.6 per 100,000. This level is significantly lower than previous nadirs in 1983 (9.2 per 100,000) and 1992 (9.1 per 100,000). The rate in vaccinating states declined 88% to 2.5 per 100,000 compared with 53% in nonvaccinating states (2.7 per 100,000). Declines were greater in children ages 2 to 18 years (87%) than in persons older than age 18 years (69%). Since 2001, rates in adults have been higher than in children. The authors conclude that continued monitoring is necessary to ascertain whether routine hepatitis A immunization of children in selected states continues to be implemented and low disease rates sustained.Dr. Schiff has disclosed no financial relationships relevant to this commentary.This study from the CDC and another report from Ben Gurion University in Israel3 confirm the effectiveness of hepatitis A vaccination as a means to control this disease. Assessing the impact of our current vaccination strategy on trends in reported cases is complicated by the known cyclical patterns of hepatitis A incidence, with peaks each 10 to 15 years.2 Although it is not possible to quantify the relative contribution of vaccine to the decreased incidence, the magnitude of the decline since 1999 is unprecedented and has been greatest in those areas where children are vaccinated. Indeed, hepatitis A rates in those states where vaccination was recommended are now lower than in states without such recommendations. Continuing to target only children ages 2 years to 18 years in certain formerly high-incidence states may not be the optimal strategy for the US because it is unlikely to result in a substantial further decline in hepatitis A infections. Utilizing the Israeli approach of universal immunization of all children ages 18 months to 24 months without a catch-up component3 might be preferable and is worthy of further investigation.This study and its counterpart from Israel provide strong evidence for the efficacy of hepatitis A vaccine. Although young infected children frequently are asymptomatic or anicteric, they play an important role in virus transmission. Moreover, a prolonged course or relapse, as well as fulminant hepatitis, have been observed, most often in adults and those with underlying liver disease. Hepatitis A vaccine has been licensed for use in children as young as age 12 months outside the US. The lower age limit for hepatitis A immunization in the US has been 24 months, but in mid-August one manufacturer (Merck) received US Food and Drug Administration approval for administering its hepatitis A vaccine (VAQTA) to children age 12 months and older. Expanding routine hepatitis A immunization to all US children is feasible and could further reduce the individual and societal burden of this infection. The costs and benefits of such a strategy are under review by both the Advisory Committee on Immunization Practices (ACIP) and the Red Book Committee. Stay tuned.