The 2015-2016 influenza epidemic in Beijing, China: Unlike elsewhere, circulation of influenza A(H3N2) with moderate vaccine effectiveness.

BACKGROUND: While the 2015-2016 influenza season in the northern hemisphere was dominated by A(H1N1)pdm09 and B/Victoria viruses, in Beijing, China, there was also significant circulation of influenza A(H3N2) virus. In this report we estimate vaccine effectiveness (VE) against influenza A(H3N2) and other circulating viruses, and describe further characteristics of the 2015-2016 influenza season in Beijing.

METHODS: We estimated VE of the 2015-2016 trivalent inactivated vaccine (TIV) against laboratory-confirmed influenza virus infection using the test-negative study design. The effect of prior vaccination on current VE was also examined.

RESULTS: Of 11,000 eligible patients included in the study, 2969 (27.0%) were influenza positive. Vaccination coverage was 4.2% in both cases and controls. Adjusted VE against all influenza was 8% (95% CI: -16% to 27%): 18% (95% CI: -38% to 52%) for influenza A(H1N1)pdm09, 54% (95% CI: 16% to 74%) for influenza A(H3N2), and -8% (95% CI: -40% to 18%) for influenza B/Victoria. The overall VE for receipt of 2015-2016 vaccination only, 2014-2015 vaccination only, and vaccinations in both seasons was -15% (95% CI: -63% to 19%), -25% (95% CI: -78% to 13%), and 18% (95% CI: -11% to 40%), respectively.

CONCLUSIONS: Overall the 2015-2016 TIV was protective against influenza infection in Beijing, with higher VE against the A(H3N2) viruses compared to A(H1N1)pdm09 and B viruses.