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Influenza

Flu Vaccine Effectiveness: What the Data Shows

Effectiveness varies year to year depending on how closely the vaccine’s formulation matches the circulating strains — understanding this helps set realistic expectations rather than treating vaccination as a guarantee.

Why effectiveness varies

Flu vaccines are reformulated annually based on WHO recommendations, made months ahead of the season based on predicted circulating strains. When the prediction matches well, effectiveness tends to be higher; when the virus drifts unexpectedly, effectiveness can be lower. Published seasonal effectiveness figures typically range widely year to year — check current CDC or WHO data for the specific season in question rather than relying on a fixed figure here.

What “effectiveness” actually measures

Even in lower-effectiveness years, vaccination is generally associated with reduced illness severity and complication risk among those who still contract flu, not just outright prevention. This is a personal health decision best discussed with a healthcare provider — we don’t offer vaccination guidance here.

Regardless of vaccination status, workplace-level prevention — hygiene, sick leave, background disinfection — remains relevant every season; see staying healthy this flu season.