Abstract: Objective To understand the protective effect of tetravalent influenza vaccine inoculated in autumn and winter of 2018 in Beijing on influenza A H3N2.Methods Data of 2 successive H3N2 influenza outbreaks in a primary school in Haidian District in December 2018(including influenza vaccination and laboratory test reports) were collected and analyzed to calculate the protection rate.Results The attack rate of 2 outbreaks was 44.63%(54/121) and 25.40%(32/126),respectively,and the positive rates of H3N2 nucleic acid were 77.27%(34/44) and 70.83%(17/24),respectively. There was no significant difference between the 2 outbreaks(χ²= 0.343,P=0.558). The protective rates of influenza vaccine against H3N2 were 12.32% and-11.35%,respectively. There was no significant difference in the incidence of H3N2 between the vaccination group and the non-vaccination group in outbreak 1 and 2(χ²= 0.204,P=0.652; χ²<0.001,P=1.000).Conclusions The protective effect of tetravalent influenza vaccine inoculated in autumn and winter of 2018 in Beijing on influenza A H3N2 is not obvious. Influenza prevention and control cannot rely entirely on vaccines,but also need a variety of comprehensive measures.