Where Did Omicron Come From? Maybe Its First Host Was Mice

One of the mysteries of the Covid epidemic is where Omicron came from. The fast- moving variant arrived just after Thanksgiving. Scientists untangled the array and discovered that Omicron wasn't related to Delta or Alpha. The first few months of the pandemic were when the divergence from its closest common ancestor occurred.

It was a dilemma. It ripped through more than 120 countries in two months, yet have not been detected for a long time. There was a puzzle about where Omicron hid all that time.

There were competing hypotheses that it had taken shelter in a group of people who had little contact with the outside world and no involvement in genome research. The home it found was so immunocompromised that they couldn't overcome the infection and give up the virus territory. It fell back into the animal world, not into the bats in which it first found a host, but into some new species that would cause a lot of change.

It was already a known risk when it came to reverse zoonosis. In April 2020, just a few months after the virus began spreading internationally, it migrated into mink farms in the Netherlands, triggering the deaths or preventive slaughter of millions of animals.

With Omicron spinning off variant after variant, no one has been able to say which of the three hypotheses is responsible for Omicron's arrival. The debate is getting fresh energy from a new study. The analysis shows that Omicron developed its array before it reached humans.

Senior author Fang Li, a professor of pharmacology and director of the university's Center for Coronaviruses Research, said in a statement that the Omicron mutations are evolutionary traces left by the virus. Li did not want to be interviewed.

In the study, published last week in the Proceedings of the National Academy of Sciences, researchers took a structural biology approach to examine the shapes of molecule within the virus. The virus was more efficient in binding to the ACE2 in the cells of mice than it was in the humans. The binding of non-infectious pseudoviruses to cells engineered to include the mouse or human receptors was confirmed by assembling them. Omicron was more fond of the mouse version.