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

• Published in: The Journal of infectious diseases 2018-04, Vol.217 (9), p.1365-1371
• Main Authors: Chiu, Susan S, Kwan, Mike Y W, Feng, Shuo, Wong, Joshua S C, Leung, Chi-Wai, Chan, Eunice L Y, Chan, Kwok-Hung, Ng, Tak-Keung, To, Wing-Kin, Cowling, Benjamin J, Peiris, J S Malik
• Format: Article
• Language: English
• Subjects: Major and Brief Reports
• ISSN: 0022-1899; 1537-6613
• DOI: 10.1093/infdis/jiy027

Abstract Background 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. Methods 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. Results 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. Conclusions Influenza vaccination was effective in preventing hospitalizations in children in Hong Kong. We conducted a test-negative study in children in 3 Hong Kong hospitals in 2016/2017. We estimated that influenza vaccine effectiveness against hospitalization due to influenza A(H3N2) was 39.7% (95% confidence interval, 14.7%–57.3%).