Risk of reinfection with omicron three times higher than previous variants, study finds

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Covid-19 cases in South Africa are rising dramatically, with experts concerned that the new omicron variant is spreading fast - Bloomberg
Covid-19 cases in South Africa are rising dramatically, with experts concerned that the new omicron variant is spreading fast - Bloomberg

The risk of reinfection from the omicron variant is three times higher than for the delta and beta strains of Covid, a preliminary study has shown.

A large-scale South African study of nearly three million people infected with Covid, published on the Medrxiv website, said the risk of infection had been stable during previous waves of the virus but this risk increased three-fold between October and November when the omicron variant was thought to have first emerged.

“The timing of these changes strongly suggests that they are driven by the emergence of the omicron variant,” the paper said.

The authors concluded: “Evidence suggests that the omicron variant is associated with substantial ability to evade immunity from prior infection.”

Professor Juliet Pulliam, director of the South African Centre for Epidemiological Modelling and Analysis at Stellenbosch University and lead author of the paper, said: “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.”

The study authors added there were still “urgent questions” about whether omicron was able to evade vaccines.

Omicron was first detected in Botswana and South Africa last week, and is believed to be behind a surge in cases in South Africa.

The variant has now spread to at least 23 countries globally and the WHO has said it is a "very high" global risk, with scientists scrambling to find out how transmissible it is and how dangerous, as well as the extent to which it can evade existing immunity.

The study added: “If the high number of reinfections in Gauteng and nationally indicates that Omicron is able to evade immunity from prior infection, this pattern should become clear across provinces by early-to-mid December.”

Dr Harry Moultrie, senior medical epidemiologist at the National Institute for Communicable Diseases in South Africa, said the findings have important implications for countries that have a high rate of immunity from prior infections and low vaccine coverage.

“Our most urgent priority now is to quantify the extent of omicron’s immune escape for both natural and vaccine-derived immunity, as well as its transmissibility relative to other variants and impact on disease severity,” he said.

Earlier on Thursday Professor Anne von Gottberg, a microbiologist at South Africa's National Institute for Communicable Diseases, told a World Health Organization press briefing that reinfection with omicron was more likely.

"Previous infection used to protect against delta [currently the dominant coronavirus variant globally], but now with omicron that doesn't seem to be the case."

Professor Gottberg did say that so far reinfections were leading to only mild symptoms, which also seems to be the case for vaccinated patients who catch the new variant.

For example, Israeli doctor Elad Maor, who believes he was infected with omicron while at a conference in London despite being triple jabbed, said he had "flu-like" symptoms for 48 hours. He also passed the infection on to a colleague.

On Wednesday, the WHO's Covid-19 technical lead Maria Van Kerkhove said that their data showed that "some" patients present with mild disease, although she said that they had seen reports ranging from mild to severe.

"It's early days," she said, adding that more data on transmissibility at least should be available in the coming days. Other information, including on disease severity and immunity, is expected in the next few weeks.

Meanwhile, scientists at Imperial College London have found that a person’s protection against Covid varies depending on which strain of the coronavirus they had in the past.

In a study of more than 700 healthcare workers in the UK, double-jabbed people who caught alpha were found to have lower immunity against the original strain and beta than people who caught the virus first seen in Wuhan.

However, those infected with alpha did have more immunity against delta. It is unknown which strain will give the best protection against omicron.

The variant has sparked global alarm because it has a large number of mutations, some of which have appeared in previous variants and increased the transmissibility of the virus, or reduced to a certain extent how well vaccines protect against infection.

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