Omicron may have emerged from mice, researchers discover

The SARS-CoV-2 variant B.1.1.529 was called “Omicron” by the World Health Organization (WHO) in November 2021, making it the fifth variant of concern (VOC) to emerge since the epidemic began.

Scientists have been eager to understand more about Omicron and its origins, given the virus’s rapid proliferation and emergence as the dominant strain in many nations. They were able to discover that Omicron originated from a strain that was circulating in mid-2020, but they were unable to track down any intermediate forms as Omicron grew into its current form. One theory is that Omicron infected an animal, and the mutations appeared as the virus moved through the animal population before transferring to humans.

A recent study published in KeAi’s Journal of Biosafety and Biosecurity, appears to support that animal theory. The research, led by Jianguo Xu from the National Institute for Communicable Diseases Control and Prevention China CDC, has found that the most likely intermediate host was a mouse.

According to Professor Xu, while much more work is needed before that theory can be confirmed, “our study calculated the average number of mutations in the five VOCs and investigated the key mutations in the viral S protein, where the infection originates. We found that the Omicron variant contains mutations at five key sites of the protein: K417, E484, Q493, Q498, and N501.

“This mutation profile shows that the virus has adapted to infect the cells of mice. In addition, the time-scaled phylogenetic tree shows that the Omicron and Gamma lineages were likely circulating in mid-2020, which supports the hypothesis that Omicron may have evolved in a non-human animal species. We believe that the coronavirus slowly accumulated mutations over time in mice, before it was transmitted back to humans by reverse zoonotic.”

He added: “These findings suggest that researchers should focus on SARS-CoV-2 variants isolated from wild animals, especially rodents. If Omicron is determined to have been derived from mice, the implications of it circulating among non-human hosts will pose new challenges in the prevention and control of the epidemic.”