COVID-19

Omicron Might Be the Worst Covid Gets When It Comes to Transmissibility, Experts Predict

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It's too soon to know if Covid's omicron variant will hasten the end of the nearly two-year-long Covid-19 pandemic. But some experts say that when it comes to contagiousness, omicron could be the "most transmissible the virus can get."

The reason: Due to "evolutionary constraints" on how many mutations and changes the virus can make, omicron could be "the ultimate version of this virus," Dr. William Moss, executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health, tells CNBC Make It.

Studies show that omicron is more than four times as transmissible as Covid's delta variant, and that it evades immunity better than delta. As long as the virus keeps spreading, Moss says, it'll continue to mutate going forward, creating more variants down the road.

But those mutations will probably be like "sons of omicron," he says — not so different that the virus can escape immunity from vaccines or previous omicron infections.

For Covid to stop spreading, a significant portion of a population needs to maintain some level of simultaneous immunity — a challenge, since so-called "natural immunity" provides inconsistent levels of protection for unpredictable amounts of time. It's estimated that 94% of the population must carry some form of immunity to interrupt the chain of transmission, according to the Mayo Clinic.

Moss' theory is "my own kind of gut feeling, and I know other people don't agree with this," he admits.

Other experts say his theory could be accurate, but it's simply too soon to tell.

"By the looks and behavior, my guess is for SARS-CoV-2, this is probably as high as it will/need climb" in terms of transmissibility, says Dr. T. Jacob John, a retired professor and head of departments of clinical virology and microbiology at CMC Vellore. But it's a waiting game to see if omicron will displace delta as fully as delta displaced variants like alpha, beta, and gamma, John says.

That matters: "If delta is replaced, then omicron has no 'biological need' to increase transmission efficiency," John says.

An early study from South Africa released in late December suggests that it's possible, citing patients who were found to have extra immunity against delta after recovering from omicron infections. But John says the scenario is unlikely. Instead, he suspects that both variants could stick around long enough to circulate as endemic viruses going forward.

"[F]uture mutations may be based on them," he says.

For Dr. David Ho, a world-renowned virologist and Columbia University professor, any prediction of Covid's future requires a healthy amount of caution. Covid "has surprised us every few months," he says.

Ho's metaphor to prove his point: When famed American sprinter Carl Lewis ran the 100-meter dash, "he was so impressive that it was hard to imagine anyone running faster. Then came Usain Bolt."

In other words, Ho says, predicting whether the pandemic's severity will peak with omicron is a challenge. "I agree there has to be a limit," he says. "But has that been reached by omicron?"

Dr. Bruce Farber, chief of infectious diseases at New Hyde Park, New York-based hospital network Northwell Health, agrees: While omicron is extraordinarily contagious, he says, the virus' future remains uncertain.

"This virus has taken so many unprecedented turns. I would be reluctant to conclude that it is the ultimate variant at this time," Farber says.

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