Deer helped spread COVID to humans, new U.S. study finds 

COVID-19 might have spread from deer to humans, according to a new study published on Monday that examined thousands of samples collected from the animals.

The analysis is part of a multiyear federal effort by the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service to study how the virus affected wildlife in the nation. 

As part of the study, researchers analyzed 8,830 respiratory samples from white-tailed deer across 26 states from November 2021 to April 2022 to compare how the virus found in the deer compares against other publicly reported samples of human infections around the world. 

Through the analysis, researchers were able to identify 109 “independent spillover events,” or viruses that matched the samples collected by the deer and humans. 

Additionally, researchers found that several deer contracted the virus from humans, including the Alpha, Gamma, and Delta variants, which then mutated and spread between the wild deer population. 

"Overall, this study demonstrated that frequent introductions of new human viruses into free-ranging white-tailed deer continued to occur and that SARS-CoV-2 VOCs were capable of persisting in white-tailed deer even after those variants became rare in the human population," the study's authors wrote.

Furthermore, after the virus had mutated within the deer a so-called “spillback” took place, which passed the new mutated virus from the deer back to humans. Two of the spillback cases were found in North Carolina and one in Massachusetts. 

While the transmission of the virus from deer to humans is still relatively small, the spread of the virus between animals and humans raises several public health concerns. 

“Deer regularly interact with humans and are commonly found in human environments — near our homes, pets, wastewater, and trash,” Xiu-Feng Wan, an expert on zoonotic disease at the University of Missouri and an author of the new paper, said in a statement.

“The potential for SARS-CoV-2, or any zoonotic disease, to persist and evolve in wildlife populations can pose unique public health risks.”