There appears to be a higher risk of catching COVID-19 again with the Omicron variant, according to a study by South African scientists that has not yet been peer-reviewed.
Researchers analysed 35,670 cases of reinfection out of nearly 2.8 million people who tested positive for COVID-19 in South Africa.
The risk of reinfection was much higher in November amid a surge in cases attributed to the newly identified Omicron variant.
"Population-level evidence suggests that the Omicron variant is associated with substantial ability to evade immunity from prior infection," the researchers said.
The World Health Organization had already warned that preliminary evidence showed a higher risk of reinfection with the new variant.
Scientists are working to determine if the variant is likely to infect people who are vaccinated against the virus but determining this could take some time.
It is also too early to determine if there is a bigger threat of severe illness with this new variant, experts say.
Professor Barry Schoub, virologist and head of South Africa's ministerial advisory committee on COVID-19, told Sky News that the early evidence was "promising" on vaccines protecting against the variant.
"It's still early days (to determine if Omicron variant carries a bigger threat of serious illness and death), and I think we need to reserve judgment on that," he said.
"Certainly in this early stage, the news does look to be promising. The great majority of the breakthrough infection, in other words, individuals that have had an infection despite vaccination, is mild."
South Africa has faced a surge of infections due to the new Omicron variant, with more than 11,000 new cases reported and 44 deaths in 24 hours. It represented a nearly 35% increase in infections in just a single day.
The country is ramping up its vaccination campaign to tackle the surge in cases.