Change in hepatitis A epidemiology after vaccinating high risk children in Taiwan, 1995-2008

Taiwan started to immunize children in 30 indigenous townships against hepatitis A since June 1995. The program was further expanded to 19 non-indigenous townships with higher incidence or increased risk of epidemic in 1997-2002, covering 2% of total population. Annual incidence of hepatitis A decreased from 2.96 in 1995 (baseline period) to 0.90/100,000 in 2003-2008 (vaccination period). The incidence in vaccinated townships and unvaccinated townships declined 98.3% (49.66-0.86/100,000) and 52.6% (1.90-0.90/100,000). In 2003-2008, incidence doubled in people aged >=30 years, mostly in unvaccinated townships (0.42-0.92). During 2003-2008, travel to endemic countries was the most commonly reported risk factor (13.5%). First dose vaccine coverage was 78.8% in 1994-2005 birth cohort. Taiwan's experience demonstrates the great, long-term efficacy of hepatitis A vaccine in disease control in vaccinated townships, and out-of-cohort effect in unvaccinated townships. Further reduction can be achieved by improving vaccination coverage of adults at risk.