The Coronavirus (COVID-19) omicron variant has a "substantial" ability to evade immunity from previous infection, a new study found.
The findings of the study, carried out by researchers at South Africa's National Institute for Communicable Diseases (NICD) and reported on Sky News, suggest omicron could cause a wave of infections, even in populations with high levels of antibodies.
The scientists said questions still remain about whether Omicron is also able to evade vaccine-induced immunity.
The study looked at 2.8 million confirmed COVID-19 cases in South Africa since March 2020 and found 35,670 were reinfections.
The risk of a reinfection was lower in the beta and delta waves than the first surge of cases in March 2020 that was caused by the Wuhan strain of the virus.
But the risk of reinfection in the current omicron wave is 2.4 times higher than in the first wave, the study found.
Professor Paul Hunter, of The Norwich School of Medicine, University of East Anglia, told Sky News: "The implications of this paper are that omicron will be able to overcome natural and probably vaccine induced immunity to a significant degree.
"But, the degree is still unclear, though it is doubtful that this will represent complete escape.
"The other big uncertainty is whether this increases the risk of severe disease, hospital admissions and deaths.
"With previous variants, epidemiological studies showed that protection against severe disease from other variants was better maintained than protection against infection."