Adverse events during mass vaccination campaigns have had a profoundly negative impact on vaccine coverage rates. The objective of the study was to identify the characteristics of reported psychogenic illness cases following mass vaccination that needed further interventions of the national immunization program.

We collected documents that were submitted to the Korea Centers for Disease Control and Prevention for vaccine injury compensation, and analyzed cases of psychogenic illness following pandemic influenza A (H1N1) vaccination in 2009 which were confirmed by the Korean Advisory Committee on Vaccine Injury Compensation.

During the 2009-2010 influenza season, 13 million Koreans were vaccinated against pandemic influenza. Of 28 reported psychogenic illness cases following immunization, 25 were vaccinated through school-located mass immunization. Significant numbers of them were female adolescents (68%) or had underlying vulnerable conditions or emotional life stressors (36%). They required lengthy hospitalization (median, 7 days) and high medical costs (median, US $1,582 per case).

Health authorities and organizers of future mass vaccinations should be well aware of the possible occurrence of psychogenic illness, acknowledge their detailed characteristics, and take its economic burden into account to mitigate the risk of transmission of infectious diseases efficiently.