A new large meta-analysis of flu vaccine effectiveness (VE) studies conducted from 2017 through 2022 shows an average VE of 41.4% for the annual flu shot, with highest protection offered against the H1N1 strain and the lowest against the H3N2 strain. The study was published last week in Vaccine.
A total of 191 studies estimating seasonal VE for 1,221,809 participants were included in the final analysis.
In total, pooled VE was 41.4% (95% confidence interval [CI], 39.2% to 43.5%). VE was 55.4% against H1N1 (95 % CI, 52.7% to 58.1%) and 26.8% against H3N1 (95% CI, 23.5% to 29.9%).
For influenza B strains, VE was 47.2% (95% CI, 38.1% to 54.9 %) against the Yamagata lineage and 40.6% (95% CI, 23.7% to 53.7%) against the Victoria lineage, the authors said.
Younger children more protected
Overall pooled VE was 39.2% in preventing flu-associated outpatient visits and 43.7% in preventing flu-related hospitalizations.
An analysis that accounted for recipients' ages revealed that VE decreased with age across all studies. For children, pooled VE was 48.6% (95% CI, 44.7% to 52.2%). For adults aged 18 to 64 years, pooled VE was 36.7%.
Influenza vaccination provided moderate effectiveness against laboratory-confirmed influenza,
"Our study demonstrated influenza vaccination provided moderate effectiveness against laboratory-confirmed influenza, and induced comparable protection across the disease's clinical spectrum," the authors concluded.