Reduction in self-reported influenza-like-illness in school children and household members following influenza vaccine administration - a cohort study, Israel, 2016-7.

Background: Second-grade pupils in Israel have been vaccinated against influenza since the winter of 2016-2017. This study aims to appraise the rate reduction of seasonal influenza vaccine among vaccinated children and their household members, and that of the vaccinated cohort and their household members.
Methods: This retrospective cohort study was performed in winter 2016-2017 in Tel-Aviv District, Israel and compared second-grade pupils who were vaccinated at school, with third-grade pupils- who were not vaccinated at school. Parents in nine schools were asked to report prior vaccination against influenza and influenza-like illness (ILI) of their children and other household members. Rate reduction was defined as [(ILI among unvaccinated) - (ILI among vaccinated)] / (ILI among vaccinated) (%).
Results: Of 527 participants, 359 (68.1%) were unvaccinated and 168 (31.9%) vaccinated. Unvaccinated children reported more ILI compared with vaccinated children (19.5% vs. 7.7%), yielding a rate reduction of 60.5%. Unvaccinated children also had a greater number of physicians' visits and missed school days (35.7% vs. 14.9 and 42.9% vs. 25.6%, respectively). The rate of ILI among household members of unvaccinated children was 34.5%, compared with 25.0% among household members of vaccinated children. The vaccinated cohort (defined as all children in second grade) reported less ILI compared with the unvaccinated cohort (defined as all children in third grade), with a rate reduction of 44.6%. Pupils of the unvaccinated cohort were more likely to miss school days (42.1% vs. 32.0%, respectively), and a higher rate of ILI was reported among household members of the unvaccinated cohort (35.4% vs. 27.3%, respectively).
Conclusion: Influenza vaccine administered in school setting reduced ILI among the vaccinated cohort and their household members by 60.5 and 27.5%, respectively, compared with the unvaccinated cohort. Expansion of the vaccination program in a school setting increased the public health benefit of influenza vaccines among both school children and their household members.