%0 Journal Article
%T Hospital-based vaccine effectiveness against influenza B lineages, Hong Kong, 2009-14.
%A Chiu SS
%A Feng S
%A Chan KH
%A Lo JY
%A Chan EL
%A So LY
%A Cowling BJ
%A Peiris JS
%J Vaccine
%V 34
%N 19
%D Apr 2016 27
%M 27013437
%F 4.169
%R 10.1016/j.vaccine.2016.03.032
%X <B>BACKGROUND: </B>We estimated vaccine effectiveness (VE) against pediatric influenza B hospitalizations in Hong Kong year round between November 2001 and October 2014.<BR><B>METHODS: </B>We conducted a test-negative year-round study, enrolling children 6 months to 17 years of age admitted to two hospitals in Hong Kong with a febrile acute respiratory infection. Children were tested for influenza A and B. Conditional logistic regression was used to estimate overall and lineage-specific vaccine effectiveness comparing influenza vaccination history of the trivalent influenza vaccine (TIV) among patients testing positive for influenza B versus negative for influenza A and B, adjusting for age and sex and matching by calendar week of recruitment.<BR><B>RESULTS: </B>Of the 6013 children included in the analysis, 262 tested positive for influenza B. Vaccination coverage was low: 6.5% in the influenza B positive children when compared with 8.8% in children who tested negative for both influenza A and B (p=0.248). Overall, VE was 47.6% (95% CI: 10.0, 69.4%) against influenza B hospitalization despite variable co-circulation of both lineages in all years. VE for Victoria-like virus calculated from 3 years when the vaccine was lineage-matched was 59.1% (95% CI: 6.2, 82.2%). Lineage-matched VE for Yamagata-like virus was -8.8% (95% CI: -215.4, 62.5%) in a clade mismatch season. With wide confidence intervals, we were unable to demonstrate cross-lineage protection: VE against the mismatched B/Yamagata-like virus was 9.5% (95% CI: -240.4, 76.0%) in 2011/12 and against mismatched B/Victoria-like virus in 2013/14 was 42.7% (95% CI: -368.6, 93.0%).<BR><B>CONCLUSIONS: </B>TIV conferred an overall VE of 47.6% (95% CI: 10.0, 69.4%) against influenza B hospitalization in children despite variable co-circulation of both lineages in all years. Lineage-matched VE for Yamagata-like virus was poor and may be related to clade mismatch. Cross-lineage protection was not observed.