How Effective Has This Vaccination Strategy Been?
The exploration of this question begins with an appreciation of the historically high rates of morbidity and mortality resulting from hepatitis A virus (HAV) infection before the introduction of hepatitis A vaccines.
HAV infection is the most common form of viral hepatitis worldwide. It is characterized by acute onset of fever, malaise, nausea, and jaundice. In addition to foodborne outbreaks, as noted above, transmission has been associated with international travel. Cyclic outbreaks have been reported among men who have sex with men and those with a history of injecting street drugs.[3,4,5,6]
Hepatitis A is generally viewed as a mild, self-limited infection. However, in adults, the disease results in substantial morbidity, medical costs, and work loss. In 2007, 35% of those with acute HAV infection were hospitalized.[6,7] Fatality is unusual in children, but the risk increases significantly in adults older than 40 years. Mortality rates appear to be higher in patients with any underlying liver disease, such as chronic hepatitis C.
Hepatitis A vaccines are highly immunogenic, with nearly all vaccinees developing protective levels of antibody within 1 month after a single dose of the vaccine.[3,4,8] They are also highly efficacious. The introduction of hepatitis A vaccination in the United States in 1995 precipitated a dramatic decline in the incidence of HAV infection. Rates fell from 12.6 cases per 100,000 in 1990 to 0.65 cases per 100,000 in 2009.[5,6]
Let me illustrate the success of the regional strategy for children at high risk for exposure to hepatitis A with a recently published example. Arizona had the highest hepatitis A incidence of any state during 1987-1997 before the implementation of the series of hepatitis A vaccination policies and recommendations.[5,6] Erhart and Ernst documented a major shift in the overall burden of hepatitis A in Arizona since the widespread implementation of immunization policies and the concomitant rise in vaccination rates in the state. Overall, the incidence of HAV infection in Arizona fell from 58 cases per 100,000 in 1988 to 2 per 100,000 in 2007. The proportion of reported cases among children dropped from 62% to 32%. Transmission shifted from children to older age groups, and disparities by race/ethnicity were now highest in Hispanic populations. These investigators commented that strategies to further reduce hepatitis A transmission may require broadening recommendations to include general adult populations.
The hepatitis A vaccine was also shown to be effective when given for postexposure prophylaxis. Victor and colleagues compared hepatitis A vaccine with immune globulin (IG) when administered within 2 weeks after exposure to the virus. Laboratory-confirmed, symptomatic HAV infection occurring between 15 and 56 days after exposure to HAV was documented in 4.4% of contacts receiving vaccine and in 3.3% of contacts receiving IG. The vaccine has several advantages over IG, including long-term protection, ease of administration, and widespread availability; therefore, it is a reasonable alternative to IG for postexposure prophylaxis. These results provided support for the recent change in US policy to the preference for hepatitis A vaccine over IG for postexposure prophylaxis in healthy persons 2-40 years of age, with the continued use of IG in contacts outside this age range and in those who are immunocompromised or who have chronic liver disease.[4,11]
Medscape Gastroenterology © 2013 WebMD, LLC
Cite this: William F. Balistreri. Speaking of Hepatitis, We Have 'A' Vaccine - Medscape - Jul 12, 2013.