JOHANNESBURG – An early study of coronavirus cases in South Africa suggests that, so far, Omicron appears to be causing lower hospitalization rates than previous versions of the virus.

The study – which was published on Tuesday and is based on just three weeks of data – indicates less severe disease of the new variant, but also shows declining vaccine effectiveness and a higher risk of breakthrough infections for Omicron. Epidemiologists have warned that data for a few more weeks would be needed to draw firmer conclusions, in part because the variant has not yet spread widely and because only a small percentage of those infected get sick enough to be hospitalized. .

The study, carried out by a private health insurance company, offers a preliminary overview of the effect of the Omicron variant, but there are other possible explanations for the observed trends. For example, infections may appear to be milder overall, as more people in this wave have some protection from a previous infection or vaccination.

Additionally, the average age of those in the study was 34, and young people generally tend to have mild symptoms. It can also make Omicron appear sweeter than it is.

The findings echo existing data which shows that while new coronavirus cases have increased exponentially, the trajectory of hospital admissions has been much flatter.

A snapshot of the first three weeks of each of the four waves of infection shows hospital admissions to be significantly lower during the Omicron-led fourth wave – 38 admissions per 1,000 versus 101 during the Delta wave and 131 per 1,000 when the beta variant was dominant, the study showed.

Incidentally, those who were admitted to hospitals had much milder illness and shorter hospital stays. The majority of patients who required oxygen were not vaccinated and only 16% of ICU admissions were vaccinated.

The effectiveness of the Pfizer-BioNTech vaccine appeared to decline, falling to just 33% from 80% during the Omicron wave. Few boosters are currently available in South Africa.

“Omicron dramatically reduced the vaccine’s effectiveness against new infections, potentially worsened by diminishing durability,” the study showed.

Still, the Pfizer-BioNTech vaccine provided 70 percent protection against serious illness and hospitalization.

The study was conducted by Discovery Health, which tracked data from 211,000 positive cases nationwide and drew on anecdotal evidence from private hospitals and primary health care groups in South Africa. This means the findings are only based on a segment of society that can afford private health care, and a large majority of South Africans depend on public hospitals and clinics.

Although the study found low Covid-19 hospital admissions for children in absolute terms, it said children appeared to be at higher risk for hospitalization during the wave driven by Omicron. But some of the cases in this wave have been seen in children admitted for other reasons, perhaps giving the impression that the risk is higher than it is.

South African experience is limited due to existing immunity and vaccinations. With more than 40 percent of adults vaccinated, the study offers little understanding of the behavior of the Omicron variant in countries with low vaccination rates, said Glenda Gray, who led the trial.