Effectiveness of influenza vaccination of day care children in reducing influenza-related morbidity among household contacts

Context A growing proportion of young children in the United States participate in day care, and these children are considered to be at high risk for influenza infection. Whether vaccinating day care children reduces household transmission of influenza is not known. Objective To evaluate the effect of vaccinating day care children on reducing influenza-related morbidity among their household contacts. Design Single-blind, randomized controlled trial conducted during the 1996-1997 influenza season. Setting Ten day care centers for children of US Navy personnel in San Diego, Calif. Participants A total of 149 day care attendees (aged 24-60 months) and their families were randomized; 127 children and their 328 household contacts received 2 vaccine doses and were included in the analysis. Interventions Inactivated influenza vaccine was administered to 60 children with 162 household contacts, and hepatitis A vaccine as a control was administered to 67 age-matched children with 166 household contacts. Main Outcome Measures Information regarding febrile respiratory illnesses and related morbidity for household contacts of influenza-vaccinated vs control children (subgrouped by influenza-vaccinated and unvaccinated contacts), obtained by telephone interviews with parents every 2 weeks from November 1996 through April 1997, Results Influenza-unvaccinated household contacts (n=120) of influenza-vaccinated day care children had 42% fewer febrile respiratory illnesses (P=.04) compared with unvaccinated household contacts of control children. Among school-aged household contacts (aged 5-17 years), there was an 80% reduction among contacts of vaccinated children (n=28) vs contacts of unvaccinated children (n=31) in febrile respiratory illnesses (P=.01), as well as reductions of more than 70% in school days missed (P=.02), reported earaches (P=.02), physician visits (P=.007), physician-prescribed antibiotics (P=.02), and adults who missed work to take care of ill children (P=.04), Conclusions These results indicate that vaccinating day care children against influenza helps reduce influenza-related morbidity among their household contacts, particularly among school-aged contacts. Future studies should be conducted in civilian populations to assess the full effect of vaccinating day care children against influenza.