Humans transmitted the coronavirus to white-tailed deer more than 100 times in late 2021 and early 2022, according to new research led by the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service. The research also suggests that the virus probably spread widely among deer, that it mutated in the animals and that they may have passed these altered versions of the virus back to people at least three times.

The findings, some of which were also published in the journal Nature Communications, add to concerns that deer, which are ubiquitous in the United States, might become a long-term animal reservoir for the virus and a potential source of new variants.