Early data from South Africa suggests that, while the omicron variant spreads remarkably quickly, it may cause relatively mild Covid-19 symptoms. But some public health experts warned omicron may appear mild only because—so far—it's spreading in populations that already have widespread natural immunity from prior coronavirus waves.

The omicron variant: The 'good,' 'bad,' and 'ugly' scenarios

Omicron spreads fast

Omicron has so far been detected in at least 30 countries on six continents, the New York Times reports. On Monday, the British government said it had detected 336 cases, more than double the number on Friday. And in Denmark, 261 omicron cases were reported on Monday, quadruple the number from Friday.

Webinar series: 'Stay Up to Date' on the latest with Covid-19

In South Africa, President Cyril Ramaphosa said omicron is spreading faster than ever. "As the country heads into a fourth wave of Covid-19 infections, we are experiencing a rate of infections that we have not seen since the pandemic started," he said.

"Nearly a quarter of all Covid-19 tests now come back positive," Ramaphosa added. "Compare this to two weeks ago, when the proportion of positive tests was sitting at around 2%."

A recent research letter from researchers at the University of Hong Kong published in the journal Emerging Infectious Diseases provided anecdotal evidence showing how easily omicron can spread. The researchers identified a case where the omicron variant spread between two people who were fully vaccinated and staying in different hotel rooms on the same corridor.

Footage from closed-circuit television in the hotel showed that neither person left their room nor had any contact with the other. As such, the virus most probably spread through the air while their room doors were open for food collection or Covid-19 testing, the researchers said.

Early reports suggest omicron may cause milder disease

While the variant is able to spread quickly, early reports from South Africa suggest omicron is causing milder cases of Covid-19 than previous variants.

One report, written by Fareed Abdullah, director of the office of AIDS and TB research at the South African Medical Research Council, looked at 42 people hospitalized at the Steve Bitko/Tshwane District Hospital Complex in Pretoria, South Africa, on Dec. 2.

It found that the majority of those patients were hospitalized for reasons unrelated to Covid-19, meaning that their infection status was "an incidental finding … largely driven by hospital policy requiring testing of all patients."

Further, 29 of the 42 patients, or 70%, were able to breathe ordinary room air—and of those receiving supplemental oxygen, four were doing so for reasons unrelated to Covid-19.

On the whole, the data suggests that these patients suffered less severe forms of Covid-19 than those infected by other variants, a finding that Abdullah said made him "cautiously optimistic."

"Two-thirds of our [Covid-19] patients … over the last two weeks are there for another diagnosis," Abdullah added. "That's unusual, that's different from previous waves."

Other hospitals in South Africa have reported similar findings. On Dec. 3, Helen Joseph Hospital said it had 37 patients in its Covid-19 ward, of whom 83% were breathing room air. Meanwhile, Dr. George Mukhari Academic Hospital reported having 80 Covid-19 patients, 81% of whom were breathing room air.

And while some hospitals in South Africa are reporting seeing more children in the hospital with Covid-19, most cases have been mild. Ntsakisi Maluleke, a public health specialist in the Gauteng province of South Africa, said, "We are comforted by clinicians' reports that the children have mild disease."

Why some experts warn early data could be misleading

However, some public health experts warned that the early data from South Africa could be misleading.

'The Never Again Plan': Moderna CEO Stéphane Bancel wants to stop the next Covid-19—before it happens

Emily Gurley, an epidemiologist at Johns Hopkins Bloomberg School of Public Health, described South Africa as having "a particular population with a particular profile of pre-existing immunity." The country has suffered from prior, severe waves of Covid-19, so many people in the population have pre-existing natural immunity to the coronavirus.

Former FDA commissioner Scott Gottlieb during a Dec. 5 interview on CBS News said, "Right now, all the evidence is that a lot of the people who are presenting with infection from this new variant are people who have been previously infected with [the delta variant]." He added, "Probably more than 90% of people in South Africa who are unvaccinated were infected with delta."

As such, he said, "[W]e don't know whether or not this new strain is inherently less virulent … or whether it's presenting that way simply because it's infecting people who already have some pre-existing immunity."

And even if omicron causes milder disease than other variants, its sheer transmissibility could make it a major health problem, according to Maria van Kerkhove, an epidemiologist at the World Health Organization.

"Even if we have a large number of cases that are mild, some of those individuals will need hospitalizations," she said. "They will need to go into ICU and some people will die. … We don't want to see that happen on top of an already difficult situations with delta circulating globally." (Fiore, MedPage Today, 12/6; Johnson, Associated Press, 12/5; Gale, Bloomberg, 12/5; Chutel et al., New York Times, 12/6; Winning, Reuters, 12/4; Kew/Cohen, Bloomberg, 12/3; CBS News, 12/5)