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Hospital-based vaccine effectiveness against influenza B lineages, Hong Kong, 2009-14
Susan S Chiu1, Shuo Feng2, Kwok-Hung Chan3
1Department of Pediatrics and Adolescent Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China.
Insights
The trivalent influenza vaccine (TIV) provided moderate protection against pediatric influenza B hospitalizations in Hong Kong. However, effectiveness varied by influenza B lineage, with no cross-lineage protection observed.
Area of Science:
- Pediatric Infectious Diseases
- Vaccinology
- Epidemiology
Background:
- Influenza B poses a significant public health threat to children.
- Understanding vaccine effectiveness (VE) against influenza B hospitalizations is crucial for public health strategies.
- Hong Kong experienced co-circulation of both influenza B lineages (Victoria and Yamagata) between 2001 and 2014.
Purpose of the Study:
- To estimate the year-round vaccine effectiveness of the trivalent influenza vaccine (TIV) against pediatric influenza B hospitalizations in Hong Kong.
- To assess lineage-specific VE against Victoria-like and Yamagata-like influenza B viruses.
- To investigate the potential for cross-lineage protection.
Main Methods:
- A test-negative, year-round study design was employed involving children aged 6 months to 17 years admitted with febrile acute respiratory infection.
- Influenza A and B testing was performed on all participants.
- Conditional logistic regression was used to estimate VE, adjusting for age and sex and matching by recruitment week.
Main Results:
- Overall VE against influenza B hospitalization was 47.6% (95% CI: 10.0, 69.4%).
- Lineage-matched VE for Victoria-like virus was 59.1% (95% CI: 6.2, 82.2%) during matched years.
- Poor VE was observed for Yamagata-like virus (-8.8%; 95% CI: -215.4, 62.5%) in a clade mismatch season, and cross-lineage protection was not demonstrated.
Conclusions:
- TIV demonstrated moderate overall effectiveness against pediatric influenza B hospitalizations in Hong Kong.
- The poor performance against the Yamagata-like virus may be attributed to clade mismatch.
- The study did not find evidence of cross-lineage protection, highlighting the importance of lineage matching in influenza vaccines.
Background:
We estimated vaccine effectiveness (VE) against pediatric influenza B hospitalizations in Hong Kong year round between November 2001 and October 2014.
Methods:
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.
Results:
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%).
Conclusions:
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.
