Bell's palsy and parenteral inactivated influenza vaccine.

Concern about a possible increased risk of Bell's palsy after parenteral inactivated influenza vaccine was raised following the publication in 2004 of a Swiss study in which there was an increased risk following the nasal inactivated formulation of the vaccine. When data from passive reporting systems in the United States and the United Kingdom were examined there was some evidence of increased reporting following the parenteral vaccine. A large population based study using the General Practice Research Database (GPRD) was therefore performed to test the hypothesis that there was an increased risk of Bell's palsy in the three months following parenteral inactivated influenza vaccine. The risk was also assessed for the same period following pneumococcal vaccine and was stratified into three age groups (<45, 45-64 and 65+ years). Relative incidence (RI) estimates were calculated using the self-controlled case-series method and showed no evidence of an increased risk in the three months following parenteral inactivated influenza vaccine RI 0.92 (95% confidence interval 0.78-1.08). There was also no evidence of an increased risk in any age group or following pneumococcal vaccine. A significant increase was seen on the day of vaccination (day 0) probably due to opportunistic recording of cases.