The Oct. 3 study, “Morbidity and Mortality Weekly Report,” used data from a research network coordinated by the Pan American Health Organization that includes Argentina, Brazile, Chile, Paraguay and Uruguay. Officials often look at Southern Hemisphere countries to get a preview of how this year’s flu season might go since their winter occurs during the U.S. summer.
Here are five things to know:
- Vaccine effectiveness was 34.5% against hospitalization among high-risk groups.
- 2023’s vaccine effectiveness was 51.9%.
- The drop in effectiveness could be due to fewer cases of the strain “A(H1N1)pdm09.”
- In 2023, H1N1 dominated cases in South America, but this year there are more H3N2 cases, WHO said.
- If the U.S. sees similar patterns, vaccine effectiveness can be expected to be similar. However CDC officials still encourage the public to get the shot.
