Influenza vaccine in healthy preschool children

Background: Studies of influenza vaccination in healthy children have not definitely answered the question of their efficacy. Methods: We have carried out a randomized trial in a well selected population of healthy preschool children in Sardinia, Italy. During October 1995, 344 children aged 1 to 6 years, were randomly assigned to receive influenza vaccine (n=177) or no treatment (n= 167). Two doses of a trivalent subvirion vaccine, containing 15mg of highly purified surface antigens from the component strains A/Johannesburg/33/94-like, A/Singapore/6/86-like and B/Beijing/184/93-like were administered. Follow-up data were collected from December 1, 1995 through April 30, 1996. Results: Seroconversion was documented in 17 out of 17 children. No specific systemic symptoms or severe local reactions were observed after vaccination. Influenza-like episodes, defined by the presence of fever and cough or sore throat that lasted at least 72 hours, occurred in 63 (37.7%) of unvaccinated children and in 22 (12.4%) of vaccinated ones. The corresponding reduction in disease incidence was 67% (95% CI: 0.59-0.74). Three episodes of otitis were observed among children in the control group versus zero among vaccinated children (p=0.07). Mean duration of day care center absenteism was significantly reduced by vaccination (2.3 days in unvaccinated and 0.5 day in vaccinated children, p<0.001) Conclusions: Influenza vaccine is safe and effective in healthy preschool children. However the favourable implications of vaccination on disease rate in subsequent years have to be evaluated.