Abstract
This study summarizes passive surveillance data for adverse events following immunization (AEFI) reported to the National AEFI Surveillance System (NASS) in Zhejiang province and describes reporting trends from 2008 to 2011. AEFI reporting rates were calculated using denominator data from the Individual Immunization Information System and the Zhejiang provincial Bureau of Statistics. A total of 6,265 AEFI records were reported; the overall reporting rate was 9.2 per 100,000 doses. There were two peaks of reporting rates, which were associated mainly with the introduction of the pandemic H1N1 influenza virus vaccine (pH1N1) in 2009 and the measles-mumps vaccine (MM) campaign in 2010. The majority of the AEFI described nonserious events. Fifteen deaths were recorded, but only one was possibly related to immunization. The most frequently reported reactions were fever and injection site reaction. Vaccines distributed in Zhejiang province have proven to be generally safe. The data on AEFI surveillance provide a reference point for ongoing reporting of trends and illustrate the value of the NASS database as a surveillance tool for monitoring of AEFI.