Background There are very little evidences that influenza vaccination reduced asthma exacerbation in under-5 children and the risk of vaccination is still being discussed.

This study aimed to detect the effect of influenza vaccination on symptomatic in asthmatic under-5.

Methods A balanced RCT with 140 asthmatic day-care children with stable situation (6 to 60 months yrs), which were vaccinated with either one-dose Inactivated-trivalent Influenza vaccine or placebo was performed. They participated for only one influenza season and were followed every two weeks. We recorded when symptom scores reached a predefined severity level.

Results Exacerbation rate among vaccinated and un-vaccinated were 13% and 53%, respectively (RR=0.24, 95%CI=0.01–0.34). 48.6% of vaccinated and 768% of placebo group reported cough (RR=0.61, 95%CI=0.04–0.35). The rate of wheezing report were 20% in vaccinated and 68.6% in unvaccinated group (RR=0.25, 95%CI=0.02–2.01). The RR for dispenea was 0.36 with 95%CI that equal 0.1 to 3.65.

Conclusion In this trial we demonstrated that tolerability and efficacy of the trivalent inactivated product in under-5 children. Then this results support annual influenza vaccination in children with asthma.