Flu Vaccine Effectiveness: How Well Does It Prevent Severe Illness in Adults?
How effective is the flu vaccine at preventing severe illness?
The flu vaccine prevents 41% of influenza-related hospitalizations in adults overall. This comprehensive meta-analysis of 30 studies found that vaccination provides moderate but meaningful protection against severe influenza illness, with effectiveness varying by age group and virus strain.
The vaccine works by training your immune system to recognize and fight influenza viruses before they can cause severe illness. When circulating flu strains closely match the vaccine components, protection increases significantly. Even when there’s a mismatch, the vaccine still provides some cross-protection against related virus strains.