Field effectiveness of hepatitis A vaccine and uptake of post exposure prophylaxis following a change to the Australian guidelines.

BACKGROUND In 2009, national guidelines for hepatitis A control in Australia changed to recommend hepatitis A vaccine (HAV), instead of normal human immune globulin (NHIG), for post-exposure prophylaxis (PEP). AIMS (1) Determine whether the uptake of PEP among contacts of hepatitis A cases changed after the introduction of the new guidelines, and (2) assess the field effectiveness of the HAV used as PEP in preventing infection among contacts of hepatitis A cases. METHODS A retrospective cohort of contacts from hepatitis A cases reported to metropolitan Public Health Units in Sydney, Australia, between October 2008 and June 2010, was identified. Contacts were analysed by time period, age, PEP type, and susceptibility to hepatitis A. The relative risk (RR) of hepatitis A infection among susceptible contacts who received HAV, compared with susceptible contacts who had not received HAV, was calculated to estimate the effectiveness of the HAV when used as PEP. RESULTS The uptake of PEP by susceptible contacts increased from 76% (n=133) to 89% (n=127) after the introduction of the new guidelines. Before the change in guidelines, no one who received PEP was later reported with hepatitis A. After the change in guidelines, one of the 123 contacts who received HAV as PEP was subsequently reported with hepatitis A. However, this case was likely to have been co-exposed with a primary case. Conservatively, assuming this was a secondary case, the vaccine effectiveness of HAV was 95.6% (66.1%-99.4%). Nine of 10 incident cases of hepatitis A were contacts who did not receive any PEP. CONCLUSION The improved uptake of PEP and the high estimate of the effectiveness of HAV provides support for using HAV for PEP. The very high occurrence of hepatitis A among contacts who did not receive any PEP further highlights the importance of PEP in preventing hepatitis A infection.