Influenza vaccine effectiveness against influenza A(H3N2) hospitalizations in children in Hong Kong in a prolonged season, 2016/17. 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 Jan 16. doi: 10.1093/infdis/jiy027. [Epub ahead of print]
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 September 1 2016 and August 31 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 between 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% 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% (17.1%, 73.2%) within 3 months of vaccination, and 31.2% (-6.6%, 55.6%) 4-6 months after vaccination.
Influenza vaccination was effective in preventing hospitalizations in children in Hong Kong.