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As the world waits for studies that give a clear picture of the Omicron variant, early clinical data emerging from South Africa hint at a virus that may cause less severe cases of Covid-19.

The South African Medical Research Council posted a report Saturday of the early experiences at several hospitals in Gauteng Province, where Omicron was first spotted in the country. Strikingly, most hospitalized patients who tested positive for Covid did not need supplemental oxygen. Few developed Covid pneumonia, few required high-level care, and fewer still were admitted to intensive care.

Experts caution against reading too much into these early reports, which are based on small numbers of patients. They suggest it will take time for the true profile of the Omicron variant to come into focus. But several note that while early discussions about previous variants of concern have hinged on trying to figure out whether they caused more severe disease, with Omicron the questions relate to whether it is associated with milder infections.


The report included an analysis of 42 Covid patients in the hospital on Dec. 2 which showed that most were actually hospitalized for other medical reasons; their infections were only detected because hospitals are testing all incoming patients for Covid. Many did not have respiratory symptoms. And the average length of hospital stay was 2.8 days, far shorter than the average of 8.5 days recorded in the region over the past 18 months, the report said.

“The relatively low number of Covid-19 pneumonia hospitalizations in the general, high care and ICU wards constitutes a very different picture compared to the beginning of previous waves,” said the report, authored by Fareed Abdullah, director of the SAMRC’s office of AIDS and TB research.


Michael Osterholm, director of the University of Minnesota’s Center for Infectious Diseases Research and Policy, told STAT he has “really been impressed by the relative lack of severe illness” seen with Omicron so far. “We’re just not seeing the number of patients that have been seen in previous surges who are seriously ill, even this soon into the surge.”

Amesh Adalja, an expert on emerging infectious disease and pandemic preparedness at Johns Hopkins University’s Center for Health Security, said more data are needed but the early indications are “very intriguing.”

“It’s part of a trend of anecdotal reports that we’re hearing that the clinical spectrum seems to be more mild, especially in vaccinated people,” he said.

It appears that the Omicron variant may be more transmissible than past variants of the virus, potentially even the highly transmissible Delta variant. But it was only identified within the past couple of weeks and still makes up only a tiny fraction of  cases worldwide, so drawing conclusions at this point is a risky business.

The SAMRC report focused primarily on the experience of the Steve Biko/Tshwane District Hospital Complex in Pretoria, an area in Gauteng Province where Omicron was first seen to be spreading. Covid cases in Tshwane District have risen rapidly in recent days, with nearly 10,000 cases reported from Nov. 29 to Dec. 3. While the National Institute for Communicable Diseases of South Africa has suggested most of the recent cases in Tshwane were caused by the Omicron variant, the hospital’s testing equipment cannot confirm that to be true for all of the cases it caught.

Of the 42 Covid patients in the hospital on Dec. 2, 70% did not need supplemental oxygen. Thirteen did require oxygen, including nine who were diagnosed with Covid pneumonia. The remaining four patients were on oxygen but for other illnesses; two, for instance, had been on home oxygen before their infections.

This is not the way things in the hospital looked at the start of the three previous Covid waves that South Africa has endured, Abdullah wrote. “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 Gauteng are reporting similar statistics, the report stated. In Helen Joseph Hospital on Dec. 3, 31 of 37 Covid patients (83%) did not require supplemental oxygen. At Dr. George Mukhari Academic Hospital, 65 of 80 Covid patients (81%) didn’t require oxygen therapy; only one was on a ventilator.

Another potentially positive signal related to the clinical status of vaccinated people. Of the Covid patients in Steve Biko/Tshwane District Hospital Complex on Dec. 2, only six were known to have been vaccinated. Of nine people who had developed Covid pneumonia, eight were unvaccinated and one was a child.

“If the assumption that they provide (most likely mostly Omicron) is correct, there is an interesting observation in that there is a clear vaccination effect if you look at the data,” Marion Koopmans, head of virology at Erasmus Medical Center in Rotterdam, the Netherlands, said in an email.

The report itself suggests as much. It notes that 80% of the people in hospital with Covid over the past two weeks were under the age of 50 — which was not the case in the three earlier Covid waves in the country. “It may be that this is a vaccination effect as 57% of people over the age of 50 have been vaccinated in the province compared to 34% in the 18-to-49-year group,” Abdullah wrote.

Koopmans agreed that to date most cases of Omicron seen in South Africa and elsewhere seem to involve mild disease, but she said it is too soon to be sure that will hold up as the virus moves into different demographic populations. “Only once we have seen this spread across age groups we will be able to tell,” she said.

Osterholm and others said it will be important, too, to watch how Omicron fares in places where the Delta variant is currently causing high levels of illness, as is the case in many parts of the United States and Europe presently.

And Peter Hotez, dean of Baylor College of Medicine’s national school of tropical medicine, said we’ll have to see what kind of illness Omicron triggers in other places before drawing conclusions.

“Potentially it means that the severity of illness is less with Omicron,” he acknowledged. “But I think we have to be very cautious about making any definitive statement. Right now, it’s an interesting anecdote as much as anything else. And we’ll see as Omicron accelerates in the United States whether if falls along a similar pattern.”

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