Influenza Vaccine Effectiveness Against Influenza A(H3N2) Hospitalizations in Children in Hong Kong in a Prolonged Season, 2016/2017. J Infect Dis.

Chiu SS, Kwan MYW, Feng S, Wong JSC, Leung CW, Chan ELY, Chan KH, Ng TK, To WK, Cowling BJ, Peiris JSM. J Infect Dis. 2018 Apr 11;217(9):1365-1371. doi: 10.1093/infdis/jiy027.

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Influenza A(H3N2) viruses circulated for 12 consecutive months in Hong Kong in 2016-2017, peaking in late June and July 2017. The objective of our study was to estimate the effectiveness of influenza vaccination in preventing hospitalizations in children in Hong Kong.


We conducted a test-negative study between 1 September 2016 and 31 August 2017, enrolling children 6 months to 17 years of age hospitalized for an acute respiratory infection. Influenza was diagnosed by PCR on nasopharyngeal aspirates.


We enrolled 5514 children, including 3608 children 6 months to 2 years, 1600 children 3-5 years, and 1206 children 6-17 years of age. Influenza-associated hospitalizations occurred throughout the study year but time of vaccination of these children was also wide spread, from September 2016 to May 2017. Influenza vaccine effectiveness (VE) was 39.7% (95% confidence interval [CI], 14.7%-57.3%) against laboratory-confirmed influenza A(H3N2). In analyses stratified by time since vaccination, the VE against influenza A(H3N2) was 52.8% (95% CI, 17.1%-73.2%) within 3 months of vaccination, and 31.2% (95% CI, -6.6% to 55.6%) 4-6 months after vaccination.


Influenza vaccination was effective in preventing hospitalizations in children in Hong Kong.