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A report from a large hospital complex in Tshwane, the epicenter of the Omicron outbreak in South Africa, suggests the variant may cause less severe disease, but warns that it's too soon to draw conclusions.

Of 42 people hospitalized at the Steve Biko/Tshwane District Hospital Complex in Pretoria on December 2, 29 (70%) were not oxygen-dependent, authored by Fareed Abdullah, MD, director of the office of AIDS and TB research at the South African Medical Research Council, which published the report online.

Twenty-four of the 38 adults hospitalized in the COVID ward on December 2 were unvaccinated, eight had an unknown status, and six were vaccinated. All nine patients with COVID pneumonia were unvaccinated, including one child.

While the report stated that most patients aren't showing respiratory symptoms, and most were admitted to the hospital for other medical reasons, Abdullah noted that it's still too soon to say the variant causes milder disease, and that the picture would become clearer over the next 2 weeks.

"What's interesting this time around -- and we want to be cautiously optimistic about it -- is that most patients in the hospital are what we are calling 'incidental COVID,'" , a South African television station.

"Two-thirds of our [COVID] patients ... over the last 2 weeks are there for another diagnosis," Abdullah said. "That's unusual, that's different from previous waves."

At the start of all three previous waves, there typically "has only been a sprinkling of patients on room air in the COVID ward and these patients have usually been in the recovery phase waiting for the resolution of a [comorbidity] prior to discharge," the report stated. "The COVID ward was recognizable by the majority of patients being on some form of oxygen supplementation with the incessant sound of high flow nasal oxygen machines, or beeping ventilator alarms."

Other hospitals in the Gauteng Province are having a similar experience with "incidental COVID," the report stated. On December 3, Helen Joseph Hospital had 37 patients in its COVID ward, with 83% on room air, and Dr. George Mukhari Academic Hospital had 80 COVID patients, with 81% on room air.

Of the 13 patients in Tshwane District Hospital Complex who were on oxygen, nine of them had a diagnosis of COVID pneumonia, while the other four were on oxygen for other medical reasons (two were previously on home oxygen, one had heart failure, and one had a diagnosis of pneumocystis pneumonia).

Abdullah's report also included an analysis of the 166 new admissions at the hospital complex from November 14 to 29. While the hospital didn't do its own genetic sequencing, the South African National Institute for Communicable Disease (NICD) confirmed that nearly all the cases in the Tshwane area were due to the new variant, the report noted.

One of the most notable findings was the shorter length of stay compared with earlier waves, at just 2.8 days in the last 2 weeks compared with 8.5 days over the last 18 months.

The age profile of hospitalized patients also differed compared to the last 18 months, with 80% of the 166 admissions being in those under age 50.

"We are seeing that probably because in the older age group there are more vaccinated people, so fewer older people getting into the hospital," Abdullah told the television station.

Indeed, 57% of people over age 50 in the province are vaccinated compared with 34% of those in the 18-to-49 age group, the report stated.

Finally, there were 10 deaths in the last 2 weeks, accounting for 6.6% of the 166 admissions, which was lower than the 17% mortality rate seen over the last 18 months.

The data from the hospital coincide with information released by the country's National Department of Health , that showed younger people are going to the hospital at a higher rate during this wave than with the previous Delta wave.

The health department also had limited data on vaccination status, but of 1,351 hospitalizations, 23% were unvaccinated and 2% were vaccinated (the majority was unknown).

"Until we can get more complete data, I wouldn't come to sweeping conclusions with this," Katelyn Jetelina, PhD, MPH, an epidemiologist at UTHealth School of Public Health in Dallas, regarding the health department data. "But it's welcoming news that the vaccinated aren't piling up at the hospital."

Jetelina also called attention to another piece of data, , by a large collaboration of researchers from South Africa's NICD and several South African universities, which she says .

It found that the rate of reinfection with Omicron is three times higher than with Delta, based on a national dataset of all positive coronavirus tests in South Africa obtained from March 2020 to November 27 this year.

"In other words," Jetelina wrote, "infection-induced immunity is not doing a great job at stopping Omicron."

Carlos del Rio, MD, of Emory University in Atlanta, told CNN on Monday afternoon that the early data on severity were promising, but that "we need to wait and see what happens when you get Omicron in the older population, and in a population with a lot of underlying chronic conditions, such as obesity and diabetes."

"I would continue to caution people," del Rio said, "and say that the best thing you can do is not get infected, either with Delta or Omicron."

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