According to CNN, the research team said it is too soon to know for sure, but a recent spike in second infections indicates to them that Omicron is more likely to reinfect people.
"Contrary to our expectations and experience with the previous variants, we are now experiencing an increase in the risk of reinfection that exceeds our prior experience," Juliet Pulliam from Stellenbosch University was quoted as saying.
Omicron was only identified in November but has worried the World Health Organisation (WHO) and other global health officials, who have designated it a variant of concern because of its many mutations affecting areas associated with transmissibility and ability to evade the immune system.
Pulliam and her colleagues looked at reports of infections covering 2.7 million people in South Africa since the beginning of the pandemic, including more than 35,000 people diagnosed more than once with Covid-19.
"We identified 35,670 individuals with at least two suspected infections (through 27 November 2021), 332 individuals with suspected third infections, and one individual with four suspected infections," they wrote in their report, posted online in a preprint.
"Among the individuals who have had more than one reinfection, 47 (14.2 per cent) experienced their third infection in November 2021, which suggests that many third infections are associated with transmission of the Omicron variant," they added.
They are assuming the recent uptick in cases in South Africa reflects the spread of Omicron and not some other factor such as waning immunity.
The people whose cases they describe have not had the virus sequenced, so it is not certain they were, in fact, infected with the Omicron variant.
However, officials said the Omicron variant is now the dominant coronavirus strain in South Africa, accounting for 74 per cent of samples that were genetically sequenced in November. More sequencing is underway to determine the true prevalence of the variant.