A study conducted by Yale researchers found a significant partisan divide in COVID death rates after vaccines became available.

A team of Yale researchers has found that Republican voters in two U.S. states had more excess deaths than Democratic voters after vaccines for COVID-19 became widely available to counter the disease. The discrepancy didn’t exist prior to the vaccines.

Jacob Wallace, assistant professor of public health (health policy); Jason L. Schwartz, associate professor of public health (health policy); and Paul Goldsmith-Pinkham, assistant professor at the Yale School of Management conducted the research using a novel linkage of political party affiliation and mortality data to assess whether there were differences in COVID-19 excess death rates between Republican and Democratic voters. The authors estimated excess death rates as the percentage increase in deaths above expected deaths due to seasonality, geographic location, party affiliation, and age.

The study found that overall, the excess death rate for Republican voters was 5.4 percentage points, or 76%, higher than the excess death rate for Democratic voters. After COVID-19 vaccines became widely available, the excess death rate gap between Republicans and Democrats widened from 1.6 percentage points to 10.4 percentage points.

“The gap in excess death rates between Republicans and Democrats is concentrated in counties with low vaccination rates and only materializes after vaccines became widely available,” the authors said in the study.

The study’s findings were recently released as a working paper by the researchers in collaboration with the National Bureau of Economic Research. The findings have been reported extensively in national media including The New York Times, The Washington Post, and NBC News.

Schwartz said the findings amplify the critical importance of vaccines.