Active surveillance of adverse events following immunization against pandemic influenza A (H1N1) in Korea.

Surveillance of vaccine safety is one of the public health interventions used to investigate the causal relationship between vaccines and adverse events. Using active surveillance data, we aimed to compile a detailed summary describing the safety of the pandemic influenza A (H1N1) vaccine. Computer-assisted telephone interview was used to investigate adverse events for 9,000 subjects who had received non-adjuvanted vaccines between November 2009 and January 2010, and for 19,000 adults who received adjuvanted vaccines from January through March 2010. The participants were interviewed to obtain information about local and systemic adverse events. Among subjects who received the non-adjuvanted vaccine, 5.5% (n=492) reported adverse events after vaccination, while 6.7% of those who received the adjuvanted vaccine reported adverse events. In the group receiving the adjuvanted vaccine, the highest reported rate of adverse events was among persons aged 19-49 years (9.1%, 577/6,329), followed by persons aged 50-64 years (7.2%, 485/6,718), and elderly persons aged 65 years and over (3.4%, 204/5,953). The implementation of this active surveillance study demonstrated the safety of both the adjuvanted and non-adjuvanted H1N1 vaccines.