A study of US prison deaths at the height of the Covid-19 crisis in 2020 has found that mortality rates soared by 77% relative to 2019, or more than three times the increase in the general population.

The study, published by Science Advances last week, is the most comprehensive analysis of in-custody deaths since 2020. The report found that “Covid-19 was the primary driver for increases in mortality due to natural causes; some states also experienced substantial increases due to unnatural causes.”

The report was compiled using data from record requests and some publicly available data, when necessary, from 49 state and federal departments of corrections.