The changing epidemiology of hepatitis A virus infections in the United States.

Abstract

The epidemiology of hepatitis A Virus (HAV) infections has changed dramatically since HAV vaccines were licensed in the United States in the mid 1990s. In 1996, after HAV vaccines became available, the Advisory Committee for Immunization Practices (ACIP) of the Centers forDiseaseControl andPrevention (CDC) recommended routine immunization of selected groups at high risk of HAV infection, including travelers to HAV-endemic countries, several other risk groups, and persons with chronic liver disease [1]. In 1999, the ACIP revised their recommendations to include immunizing all children >2 years of age living in states or communities reporting ≥2 times the national annual average incidence of HAV infection (ie, communities with >20 cases per 100 000 population). In addition, states where the reported rates of HAV infection were above the national average (ie, states with 10–19 cases per 100 000 population) were advised to consider routine immunization of 2-year-old children [2]. In 2006, the ACIP changed their recommendations again to administer HAV vaccine, together with routinely administered vaccines, to all children at 1 year of age. In addition, the committee recommended continuing immunization of persons in special populations at high risk of exposure, travelers to countries where HAV is highly endemic, and persons with chronic liver disease [3]. As a result of the routine use of HAV vaccine in children, the incidence of HAV infection in the United States has decreased substantially, from 10 cases per 100 000 population in 1996 to 0.4 cases per 100 000 population in 2011 [4, 5]. Similar declines have occurred among adults of all ages, even older adults who were not specifically targeted to be immunized. Several other countries have experienced similar dramatic declines in the overall incidence of reported hepatitis due to HAV infection after the introduction of routine childhood HAV immunizations. In Israel, the incidence of hepatitis from HAV decreased by >95% a few years after a program of routine immunization of children aged 1–4 years was implemented in 1999 [6]. The decreased incidence included the entire population, with a 90.6% reduction in HAV-related hepatitis among persons 45–64 years of age and a 77.3% reduction in persons >65 years of age. Although routine childhood immunization with HAV vaccines have been very effective, several countries have experienced an increase in the incidence of HAV-related hepatitis, despite improvements in environmental hygiene, and an increase in the average age (from childhood to adolescence and adulthood) of individuals with symptomatic rather than subclinical infections. Some of these countries have not yet adopted routine childhood use of HAV vaccines despite their remarkable effectiveness and safety record [7–9]. In this issue of The Journal of Infectious Diseases, Ly and Klevens report the trends in diseases and complications from HAV in the United States between 1999 and 2011 [4]. The data from the National Notifiable Disease Surveillance System indicated a decline in incidence, from 6.0 cases per 100 000 population in 1999 to 0.4 cases per 100 000 population in 2011. The proportion of HAV-related hospitalizations among the reported cases increased from 7.3% in 1994 to 24.5% in 2011, and the age of hospitalized cases and of cases who died increased. However, I do not understand why the authors interpreted the data to indicate a need for immunization of all adults with HAV vaccine to prevent the few remaining cases in this population. The effective implementation of such a policy would be very difficult and not cost effective. Furthermore, the incidence of HAVrelated hepatitis declined substantially in Received and accepted 19 December 2014; electronically published 29 January 2015. Correspondence: Kenrad E. Nelson, Department of Epidemiology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD (kenelson@jhsph.edu). The Journal of Infectious Diseases 2015;212:171–2 © The Author 2015. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals. permissions@oup.com. DOI: 10.1093/infdis/jiu835

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