Hepatitis A

HAV is a well-described picornavirus that has long affected populations of the world even after the availability of effective HAV vaccines since the 1990s. Highly efficacious vaccines and continuous improvements in sanitation worldwide have led to lower individual HAV seropositivity rates and a lower degree of population, or herd, immunity among nonimmunized persons, and the risk of HAV infection is therefore increased among susceptible populations. An epidemiologic shift in susceptibility from early ages to adults and older populations has occurred. In the USA and Europe, where universal pediatric vaccination has been implemented, sporadic large outbreaks of hepatitis A are on the rise in high-risk populations and older adults, who have more severe clinical manifestations than younger persons. Strategies to reduce the frequency and size of outbreaks are necessary in low endemic, low-immunity populations owing to the fact that intermediate-to-highly endemic countries continue to use targeted, regional, or sporadic mass vaccination regimens to battle this preventable viral infection.