Design: Systematic review and meta-analysis of cohort and test-negative studies
Population: 38,855 health workers in 27 studies
Primary outcome: Influenza vaccine effectiveness
Effect: Overall 34% (19–47%); laboratory-confirmed influenza 43% (22–58%)

A meta-analysis pooled 27 cohort and test-negative studies, published between 2000 and 2025, covering 38,855 health workers. Overall vaccine effectiveness was 34% (95% CI 19–47%). Against laboratory-confirmed influenza it was 43% (22–58%), and against the looser end point of influenza-like illness it was 26% (2–44%). Results from the two study designs were similar, and sensitivity analyses did not suggest publication bias.

These figures will not surprise anyone who follows influenza vaccine data, which vary by season and strain. What they give is a usable number for staff conversations: roughly four in ten laboratory-confirmed infections prevented, in a group whose infection can pass to vulnerable patients.

The included studies are observational and heterogeneous, and this analysis does not measure transmission to patients. It supports, rather than changes, existing recommendations that health workers be vaccinated each season.

Get vaccinated against influenza each season, and encourage colleagues to do the same.
Use the 43% figure against confirmed influenza when staff ask whether the vaccine is worth it.
Explain that 'flu-like illness' includes many other viruses, which is why effectiveness against it looks lower.
Stay off work when febrile with respiratory symptoms, vaccinated or not; protection is partial.
Offer vaccination to unvaccinated staff in clinical areas before the local season peaks.

Why it matters

Partial protection in staff is still fewer infected clinicians at the bedside of vulnerable patients.

The statistics, in plain English

Vaccine effectiveness of 43% means vaccinated workers had about 43% fewer confirmed infections than unvaccinated ones. The confidence intervals are wide (22% to 58%), reflecting variation between seasons and studies. Because the studies were observational, healthier or more cautious workers may have been more likely to be vaccinated.