Influenza vaccination provided moderate protection against hospitalization due to influenza in children, according to a meta-analysis published in the Clinical Infectious Diseases. Vaccination provided variable protection over seasons, by influenza type/subtype, and vaccine type.
This systematic review and meta-analysis included 37 studies that used a test-negative design to evaluate influenza vaccine effectiveness (IVE) against any influenza-associated hospitalization in children aged 6 months to 17 years old. Analyses was further stratified by influenza type (influenza A/H1N1, influenza A/H3N2, and influenza B), age group (<5 years and 6-17 years), and vaccine type (inactivated influenza vaccines and live attenuated influenza vaccines).
Of the 37 studies, 26 were from the Northern Hemisphere, 10 were from the Southern Hemisphere, and 1 was a global study. The study years ranged from 2005/2006 to 2018/2019. The overall pooled IVE was 53.3% (95% CI, 47.2%-58.8%) with moderate heterogeneity.
Heterogeneity was reduced when the data was split by season but still remained moderate to high in the 2016/17 and 2018/19 seasons. Furthermore, the results remained similar when the studies were restricted to those that only used molecular testing.
When comparing influenza type, IVE was higher for influenza A vs influenza B (58.0% [95% CI, 49.8%-64.8%] vs 35.8% [95% CI, 23.4%-46.3%]). When analyzing influenza A subtype, IVE was higher against A/H1N1 vs A/H3N2 (68.7% [95% CI, 56.9%-77.2%] vs 35.8% [95% CI, 23.4%-46.3%]).
By vaccine type, IVE was 44.3% (95% CI, 30.1%-55.7%) for live attenuated influenza vaccines. However, this was based on only 3 studies. The overall IVE for inactivated influenza vaccines was 67.1% (95% CI, 53.5%-76.8%) with quadrivalent inactivated influenza vaccines having a higher IVE than trivalent inactivated influenza vaccines (50.2% [95% CI, 10.7%-72.3%] vs 47.5% [95% CI, 39.5%-54.4%]).
IVE was higher in children 6 months to 5 years of age vs children 6 to 17 years of age (61.7% [95% CI, 54.1%- 68.1%] vs 51.7% [95% CI, 42.9%-59.1%]).
During the seasons when the circulating virus strains matched the vaccine, IVE was the highest at 59.3% (95% CI, 48.3%-68.0%); in seasons when the vaccine was mixed match to the virus strains, IVE was 58.4% (95% CI, 34.0%-73.7%).
Limitations of this study included a moderate to severe risk of bias, as well as lack of adjustment for underlying medical conditions.
“Overall, we found that influenza vaccination provided good protection against any influenza-associated hospitalisation in children aged 6 months to 17 years old,” the study authors concluded.
Boddington NL, Pearson I, Whitaker H, Mangtani P, Pebody RG. Effectiveness of influenza vaccination in preventing hospitalisation due to influenza in children: a systematic review and meta-analysis. Clin Infect Dis. Published online March 27, 2021. doi:10.1093/cid/ciab270