Epidemiology of Hepatitis A Transformed by Vaccine

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Summary and Comment

Epidemiology of Hepatitis A Transformed by Vaccine

Vaccinating toddlers against hepatitis A produces immunity throughout the population.

Since 1996, hepatitis A vaccination has been recommended in the U.S. for adults at high risk (e.g., travelers, injection drug users, men who have sex with men) and for children who live in the 17 states where disease rates were highest before a vaccine was available. This vaccination policy has dramatically changed the pattern of reported cases.

Compared with the disease rate for 1990–1997, the overall U.S. rate in 2003 had declined by 76%, to an all-time low. Rates in children (age, 2–9 years) were 89% lower than average pre-vaccine rates; in states where childhood vaccination is recommended, rates were 95% lower. Before 1997, disease was concentrated in western and southwestern states, but, by 2003, rates were uniformly low throughout the U.S. Although hepatitis A was once primarily a disease of children (whose infections fueled community-wide outbreaks), the virus now affects mostly adults.

Results of an Israeli study emphasize the importance of vaccinating the little "vectors" of this disease. In 1999, Israel adopted a two-dose vaccination program for 18- to 24-month-olds, without instituting a catch-up campaign for older children. Since then, disease rates have declined sharply, not only among vaccinated children, but also in all other age groups. Disease rates fell by 91% in 15- to 64-year-olds and by 77% in those older than 65, although only an estimated 2.5% to 5% of adults were vaccinated.

Comment: The herd protection induced by vaccinating toddlers against hepatitis A virus is dramatic and underscores the importance of pediatric immunizations in fighting this disease. The findings from this study suggest that routine immunization of all children is a reasonable way to approach hepatitis A elimination.

— Abigail Zuger, MD

Published in Journal Watch General Medicine August 19, 2005