COVID-19: Omicron variant may have originated from mice, say Chinese CDC scientists

A  study conducted by experts from the Chinese Centre for Disease and Control and Prevention has recently found that the Omicron variant of SARS-CoV-2 may have started in mice. It is to mention that the World Health Organization (WHO) classified the Omicron variant - SARS-CoV-2 variant B.1.1.529 - as a Variant of Concern (VOC) in November last year, making it the fifth VOC to arise since the start of the COVID-19 pandemic. Since then, the dissemination of the Omicron strain has been rapid since it was first identified and has become the most common variant in many regions of the world. 

Scientists across the globe have been working meticulously to uncover the true sources of the Omicron strain, which despite its high transmission rate appears to cause less severe disease than other strains of the virus, such as the Delta variant. A popular theory is that the Omicron infected an animal and that the mutations occur as it spreads among the animal population, eventually being transferred to humans. 

Origin on Omicron variant

Now, Chinese researchers have found evidence supporting the animal theory, suggesting that the most likely immediate host of the Omicron was a mouse. As per the study, Professor Jianguo Xu, the leader of the China CDC, said that the 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. Xu added that the study found that the Omicron variant contains mutations at five key sites of the protein: K417, E484, Q493, Q498, and N501. 

According to the research, the mutation profile shows that the virus has adapted to infect the cells of mice. Additionally, 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. The Chinese researchers said that they believe that the coronavirus slowly accumulated mutations over time in mice before it was transmitted back to humans by reverse zoonotic. 

“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 pandemic,” the study read. 

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