The Omicron variant has been linked to a substantial rise in coronavirus reinfections in South Africa compared with previous waves, according to the first detailed study into the heavily mutated strain that has sparked global alarm.
“Analysis of routine surveillance data from South Africa suggests that, in contrast to the Beta and Delta [variants], the Omicron variant of Sars-Cov-2 demonstrates substantial population-level evidence for evasion of immunity from prior infection,” South African epidemiologists concluded in the study published late on Thursday.
Higher reinfections detected recently were “consistent with the timing of the emergence of the Omicron variant in South Africa”, they added.
The study did not examine Omicron’s effects on vaccine-induced immunity or examine whether the reinfected cases were more likely to become severely ill.
The findings by South Africa’s National Institute For Communicable Diseases, the public health body, will alarm global health experts who have been watching the surge in cases linked to Omicron, amid fears that its unusual genetic make-up could allow it to evade immune protection from prior infection or vaccination.
Based on analysis of test results recorded up to November 27, the study — yet to be peer-reviewed — looked at people who were first infected at least three months earlier. It compared the risk of reinfection during the first wave of the pandemic with subsequent waves of different variants.
While either the Beta or Delta waves were not associated with an elevated risk of reinfection, the risk of reinfection from Omicron was 2.4 times higher, the scientists concluded. Prior infection was previously estimated to provide at least an 80 per cent reduction in infection risk.
This suggested Omicron’s “selection advantage is at least partially driven by an increased ability to infect previously infected individuals,” they added.
South Africa, which has recorded a jump in cases of the Omicron strain first detected last month, confirmed more than 11,500 new cases on Thursday, with more than one in five tests coming back positive. This is a sharp increase from the hundreds of daily infections being recorded just weeks ago.
The surge has concerned scientists because South Africa is believed to have high rates of prior infection from previous waves. But South Africa has a relatively low rate of vaccinations, with about a quarter of the population fully jabbed after a sluggish rollout in recent months.
“Urgent questions remain regarding whether Omicron is also able to evade vaccine-induced immunity and the potential implications of reduced immunity to infection on protection against severe disease and death,” the study said.
Hospital admissions have also begun to rise in Gauteng province, the centre of the outbreak. Some 788 people were admitted to hospital in the week to November 28, which is more than double the figure recorded a week earlier.
The World Health Organization, which designated Omicron a “variant of concern” late last week, has said it would take at least two weeks to understand the effects of the variant on vaccines.
While nations around the world have imposed strict travel bans to and from southern Africa in an attempt to slow the spread of Omicron, cases of the new variant have been detected in dozens of countries.
Additional reporting by John Burn-Murdoch in London