Effectiveness of inactivated influenza vaccine in children less than 5 years of age over multiple influenza seasons: A case–control study

The effectiveness of influenza vaccine over multiple influenza seasons in children less than 5 years of age has not been well studied. This is especially important to assess because of the recent recommendation for routine influenza vaccination in childhood.We conducted a matched case–control study to assess the vaccine effectiveness of Trivalent Inactivated Influenza Vaccine (TIV) against laboratory-confirmed, medically attended influenza among children 6–59 months of age at the start of each influenza season from 1999–2000 through 2006–2007 in Olmsted County, MN, USA.The children vaccinated against influenza accordingly to the 2007 ACIP guidelines had a lower risk of laboratory-confirmed medically attended influenza illness (Odds Ratio: 0.14, 95% Confidence Interval: 0.03–0.71) than the unvaccinated children. TIV provided strong protection against laboratory-confirmed medically attended influenza in children 6–59 months old in the fully vaccinated group. This trend continued in the partially vaccinated group (Odds Ratio: 0.27, 95% Confidence Interval: 0.07–0.97) but the protection provided maybe suboptimal.