South Africa’s health minister said Friday that vaccines and past infections could be a key reason that the current wave of coronavirus infections, fueled by the omicron variant, appear to be milder.

       “We believe that it might not necessarily just be that omicron is less virulent, but we believe that this coverage of vaccination, also in addition to natural immunity of people who have already had contact with the virus, is also adding to the protection,” Health Minister Joe Phaahla told a news briefing. “That’s why we are seeing mild illness.”

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       Michelle Groome, an official at the National Institute for Communicable Diseases in South Africa, told the virtual conference Friday that the country has seen a small uptick in hospital admissions and deaths. But “this level is very much lower even than the baseline period we were seeing between the second and third waves,” she said.

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       Groome added in a tweet that the disease “is likely to be milder because of our underlying immunity, rather than intrinsic virulence of the virus.” She warned that the uninfected and unvaccinated are still at risk of severe illness from the new variant.

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       Researchers have tried to understand the clinical severity of the omicron variant and vaccine efficacy against the latest variant, which has spread rapidly worldwide since last month. A private study in South Africa said this week that 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 there.

       The study by insurer Discovery Health also reported that the risk of hospital admissions among adults who developed covid-19 was 29 percent lower than in the initial coronavirus pandemic wave that emerged in March 2020.

       The World Health Organization in Africa said earlier this week that the initial stage of the current wave has led to fewer deaths than previous surges, but cautioned that the pattern may still change in the coming weeks.

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       England’s chief medical officer, Chris Whitty, cautioned Wednesday that it was possible that reduced hospitalization rates in South Africa would not be replicated in other countries. “It may be that some of, possibly even all of, any decrease in severity from South Africa is just explained by immunity,” he said adding that the different age groups of each country’s population should also be taken into account.

       “I want to be clear, I’m afraid this is going to be a problem,” he said, referring to the omicron variant. “The exact proportions of it, of course, South African scientists and U.K. scientists and scientists globally are trying to determine.”

       Helier Cheung contributed to this report.

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