In the largest population-based study of its type in the US, over 45,000 infants aged 6-23 months, who received inactivated influenza vaccine between 1991 and 2003 were included. Medically attended events after flu vaccination were reviewed for 4 different time periods, and compared with 2 control time periods. All diagnostic codes were checked.
This study showed that there were very few medically attended events and none were for serious causes associated with the vaccine. None of the 14 diagnoses made in the context of medical referral after vaccination had any statistically significant link to vaccination.
The study provides additional evidence supporting the safety of flu vaccination in children aged 6-23 months.