Reduction of acute respiratory illness (ARI) due to a voluntary workplace influenza vaccination program: who are more likely to get the benefit?

The study investigated the overall effectiveness and its determinants of an influenza vaccination in the reduction of acute respiratory illness (ARI) clinic visits and sickness absence for a working population. We collected and compared the data of clinic visits and hours of sick leave among vaccinated and non-vaccinated workers during January and April in 1998 and 1999. A multiple regression analysis was conducted to explore possible determinants. The incidence rate of ARI clinic visits dropped 37.9% in 1999, with 57.3% reduction in vaccinated and 14.1% in un-vaccinated workers. Multiple regression analysis showed that the reduction was significantly associated with vaccination status, a history of diabetes, and occurrence of ARI clinic visits in 1998. Influenza vaccination is effective in reducing ARI clinic visits and sickness absence. Workers with a previous history of ARI, diabetes, and possibly young workers living with children were more likely to get the benefit. The identification of potential susceptible subpopulations can also minimize confusion on company policy for isolation during an epidemic of new infectious disease with flu-like symptoms.