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Published on: August 14, 2019
Influenza Vaccine Effectiveness Among Children: 2011-2020
Nicole Hood1, Brendan Flannery1, Manjusha Gaglani2,3
1Influenza Division, US Centers for Disease Control and Prevention, Atlanta, Georgia.
Insights
The inactivated influenza vaccine demonstrated 46% effectiveness in children against outpatient illness across nine seasons. Effectiveness was highest in younger children (6-59 months) and varied by influenza type, with lower protection against A(H3N2).
Area of Science:
- Pediatric Infectious Diseases
- Vaccinology
- Epidemiology
Background:
- Infants and children face higher risks of severe influenza and complications.
- Influenza vaccine effectiveness (VE) is known to vary by age, season, and virus type.
- Post-2009 pandemic influenza A(H1N1) VE in children requires ongoing evaluation.
Purpose of the Study:
- To assess inactivated influenza vaccine effectiveness against outpatient influenza illness in children.
- To analyze VE across nine influenza seasons in the pediatric population.
- To identify VE variations by age group and influenza virus type/subtype.
Main Methods:
- A test-negative design was employed.
- Data collected from 24,148 children aged 6 months to 17 years across five US sites.
- Influenza testing performed using real-time, reverse-transcriptase polymerase chain reaction.
Main Results:
- Pooled VE for any influenza was 46% (95% CI, 43-50) across all seasons.
- VE was highest in the 6- to 59-month age group compared to older children.
- VE was lowest against influenza A(H3N2) virus infection.
Conclusions:
- The inactivated influenza vaccine provides substantial benefit against outpatient influenza illness in children.
- Understanding age and virus-specific VE differences can inform strategies to improve vaccination coverage.
- Further research into host-specific and virus-related mechanisms is recommended.
Background And Objectives:
Infants and children are at increased risk of severe influenza virus infection and its complications. Influenza vaccine effectiveness (VE) varies by age, influenza season, and influenza virus type/subtype. This study's objective was to examine the effectiveness of inactivated influenza vaccine against outpatient influenza illness in the pediatric population over 9 influenza seasons after the 2009 A(H1N1) pandemic.
Methods:
During the 2011-2012 through the 2019-2020 influenza seasons at outpatient clinics at 5 sites of the US Influenza Vaccine Effectiveness Network, children aged 6 months to 17 years with an acute respiratory illness were tested for influenza using real-time, reverse-transcriptase polymerase chain reaction. Vaccine effectiveness was estimated using a test-negative design.
Results:
Among 24 148 enrolled children, 28% overall tested positive for influenza, 3017 tested positive for influenza A(H3N2), 1459 for influenza A(H1N1)pdm09, and 2178 for influenza B. Among all enrollees, 39% overall were vaccinated, with 29% of influenza cases and 43% of influenza-negative controls vaccinated. Across all influenza seasons, the pooled VE for any influenza was 46% (95% confidence interval, 43-50). Overall and by type/subtype, VE against influenza illness was highest among children in the 6- to 59-month age group compared with older pediatric age groups. VE was lowest for influenza A(H3N2) virus infection.
Conclusions:
Analysis of multiple seasons suggested substantial benefit against outpatient illness. Investigation of host-specific or virus-related mechanisms that may result in differences by age and virus type/subtype may help further efforts to promote increased vaccination coverage and other influenza-related preventative measures.
