Scientists think that the omicron variant of the coronavirus likely evolved within a single immunocompromised person, USA Today reported on Monday.

"It's reasonable speculation, but we don't know for sure," said Jesse Bloom, who studies viral evolution at the Fred Hutchinson Cancer Research Center in Seattle.

Although no "patient zero" has been discovered for omicron or any other variant, studies have shown that those in treatment for cancer, immunosuppressed after an organ transplant, or weakened by HIV, can continue to be infected with coronavirus for months, while it accumulates changes that make it more difficult to eliminate.

Omicron has 50 changes from the virus’ original genetic code, including 30 on the spike proteins that are on the virus’ surface and which are the target of vaccines and some treatments.

Surveillance data suggests that these changes arrived at the same time, not one at a time as the virus goes from one person to another, which lends backing to the theory that they co-evolved within a single person.

Experts insist that it is still too early to know if all these changes will make the variant less subject to protection from vaccines and previous infections, or if it will be able to evade monoclonal antibody treatments.

"If it transmits well but doesn't replicate well in its new host, it's not as likely to win out in the end, because it's got a dead-end path," said Dr. Bruce Walker, an immunology professor at Harvard Medical School and the Massachusetts Institute of Technology.

He added that mutations that offer a survival advantage "can get into more people and create more viruses to infect more of the species."

In a normally healthy person, whose immune system gets rid of the virus in about a week, there is not so much time for mutations to accumulate, said Walker. But in an immunocompromised person, the virus might linger for months, giving the virus plenty of time to accumulate random changes that work to its advantage.

"Even within a person, you can select for increased transmissibility from one cell to another, and you can select for better replication," he said.

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