We think flu shots work great globally, but that's an illusion—almost all the data comes from wealthy countries.
March 18, 2026
Original Paper
Imbalanced Evidence Shapes Global Estimates of Influenza Vaccine Effectiveness
SSRN · 6426381
The Takeaway
Standard estimates suggest the flu shot is about 46% effective, but this study reveals those numbers come from regions like North America and Europe. When the model accounts for the missing data from low-income countries, the estimated effectiveness varies wildly from 61% down to just 13%, suggesting the vaccine may be performing far worse in the developing world than we realized.
From the abstract
Background: Estimates of influenza vaccine effectiveness (VE) are widely used to inform vaccination policy. However, the evidence underlying these estimates is imbalanced across countries. Most VE studies are conducted in high-income settings, whereas many low- and middle-income countries lack surveillance systems capable of generating VE estimates. We examined how geographic imbalance in the global evidence base may influence assessments of influenza vaccine effectiveness.<br><br>Methods: We co