CAPE TOWN, South Africa – Omicron appears to cause less severe illness than earlier variants of the coronavirus but is more resistant to the two-dose Pfizer-BioNTech vaccine widely used in South Africa, according to a major private study of the variant.

The study by Discovery Health, South Africa’s largest health insurer, showed that risk of hospital admissions among adults who contracted covid-19 was 29% lower than in the initial pandemic wave that emerged in March 2020.

Discovery Health provided conflicting information about the size of the study. In the initial release, the company said the study was based on 211,000 positive test results in South Africa, of which 78,000 were attributed to omicron. A subsequent correction to the release removed the word “positive” from the test results and said the change “does not affect any of the calculations.” Later information provided by a Discovery Health spokeswoman put the number of total cases at 78,173, of which 19,070 tests were positive during the “omicron period” from Nov. 15 to Dec. 7. The company did not respond to requests for further clarification.

The study found that the vaccine from U.S. pharmaceutical giant Pfizer and German partner BioNTech provided just 33% protection against infection, much less than the level for other variants detected in the country.

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At the same time, the vaccine may offer 70% protection against being hospitalized with omicron, the study found, describing that level of protection as “very good.”


The protection was maintained across all age groups, Ryan Noach, Discovery Health’s chief executive, told a news briefing. He said the disease may be less severe in South Africa because more than 70% of the population had already been exposed to the coronavirus.

He cautioned, however, that it was still in the early days and hospital admissions could rise sharply as the variant evolves.

“The omicron-driven fourth wave has a significantly steeper trajectory of new infections relative to prior waves,” Noach said in a statement. “National data show an exponential increase in both new infections and test positivity rates during the first three weeks of this wave, indicating a highly transmissible variant with rapid community spread of infection.”

“What is encouraging at this stage is a flatter trajectory of hospital admissions indicating likely lower severity of this wave,” he told a news briefing later.

Noach said anecdotal evidence gathered from doctors treating omicron patients outside hospitals showed a high reinfection rate and multiple breakthrough infections in vaccinated people that emerge after a short incubation period of three to four days.

Most infections are described as mild, with recoveries usually within three days, he said. The most common early symptom reported is a scratchy throat, followed by nasal congestion, a dry cough and myalgia, or aches, manifesting in lower back pain.


He said private hospitals reported that most patients were unvaccinated and many were initially admitted for non-covid-related illnesses. There was less evidence of respiratory infections in omicron-infected patients, compared to the other variants, with fewer patients requiring oxygen, Noach added.

It’s unclear to experts whether South Africa’s experience with the omicron variant will translate to other parts of the world, especially in Europe or the United States, where populations are already getting their booster shots.

South Africa has a young population that is largely unvaccinated and has high rates of previous covid-19 infections. Most of South Africa’s omicron infections have been in people between the ages of 35 to 39, according to the National Institute for Communicable Diseases, while just 36% of the country’s adult population is vaccinated.

Glenda Gray, president of the South African Medical Research Council, said it was hard to know how the virus would evolve.

“South Africa has a quite high seroprevalence of prior infection, particularly after delta, and in some parts of South Africa up to 80% of people were exposed to previous infection,” she said, adding: “We don’t think it’s a question of virulence, but more a question of exposure to vaccination and prior infection, so we would be cautious to try and interpret that this is a less virulent strain. We’ll have to see what happens in other parts of the world before we make a call on this.”

Many infectious-disease trackers are closely tracking the omicron surge in the United Kingdom and other northern European countries for indicators on what omicron might do elsewhere.


“I think it’s reasonable to extrapolate from what’s being seen in South Africa until we get evidence to the contrary,” said John Moore, an immunologist at Weill Cornell Medicine. “The evidence is there is going to be a higher degree of vaccine failure against mild infections – we’ve already seen that with delta. . . . It’s not great, but it’s not as bad as seeing massive failure that leads to hospitalization and death.”

The World Health Organization said Tuesday that omicron, which is being reported in 77 countries, is spreading at a faster rate than previous coronavirus variants and delivered a stark warning against dismissing it as mild.

WHO Director General Tedros Adhanom Ghebreyesus warned that even if data eventually confirms that omicron causes less-severe disease than other variants, the sheer number of infections could “once again overwhelm unprepared health systems.”

Tuesday’s study out of South Africa also showed doctors were reporting a higher number of children testing positive with omicron. But Shirley Collie, chief health analytics actuary at Discovery Health, cautioned that closer examination of the issue was needed. Discovery Health’s data indicated that children under the age of 18 have a 20% higher risk of admissions for complications when infected with omicron compared to the other variants, she said.

Most children infected with omicron complained of a headache, sore throat, nasal congestion and a fever, which was usually over within three days, Collie said.

The study did find “good protection” by the vaccine across a range of chronic conditions, she added, including diabetes, hypertension and heart disease, that have proved so dangerous in the course of the disease.


The research comes as omicron has become the dominant variant in South Africa less than three weeks since its existence was confirmed on Nov. 25.

In a separate briefing Tuesday, Matshidiso Moeti, the World Health Organization’s director for Africa, declared that Africa was now officially in the fourth wave of the pandemic primarily driven by omicron, with an 83% surge in new cases this week compared to the previous week.

“This is the fastest surge recorded since May last year,” Moeti said. “We are cautiously optimistic, as we are seeing fewer deaths during the early weeks of this current wave when compared to previous surges.”

In South Africa, the drop in the protection of two doses of the Pfizer-BioNTech vaccine against any symptomatic infection is similar to what a British preprint study released late last week showed, namely that it dipped below 40%.

The British study, however, could not answer pressing questions about whether vaccine protection against severe disease would erode just as steeply. The South African data provides the first hint, showing that protection against severe illness requiring hospitalization after two doses was diminished from its more than 90% protection against the delta variant but remained relatively robust, at 70%.

The Washington Post’s Carolyn Y. Johnson and Paulina Villegas contributed to this report.