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https://scmp.com/news/china/science/article/3158344/omicron-has-substantial-ability-evade-natural-immunity-south
China/ Science

Omicron has ‘substantial’ ability to evade natural immunity, South African researchers say

  • Early analysis on the new variant suggests it carries a higher risk of reinfection than other strains
  • But the scientists say urgent questions remain on vaccine-induced immunity and disease severity
A health worker speaks with a driver at a mobile testing site in Cape Town, South Africa, on Thursday. The country reported the new coronavirus variant to the WHO on November 24. Photo: Bloomberg

The Omicron coronavirus strain has shown “substantial” ability to evade natural immunity and increases the risk of reinfection, South African scientists at the forefront of researching the new variant of concern have found.

Early evidence presented by the researchers suggests the risk of coronavirus reinfection increased threefold between the beginning of October and the end of November, the period when scientists believe the new variant was on the rise.

This differed from what they observed during the spread of earlier variants in South Africa, according to the researchers from the National Institute for Communicable Diseases and other research centres.

“In contrast to Beta and Delta, the Omicron variant of Sars-CoV-2 demonstrates substantial population-level evidence for evasion of immunity from prior infection,” they said in a paper released on Thursday that has not yet been peer reviewed.

“This finding has important implications for public health planning, particularly in countries like South Africa with high rates of immunity from prior infection.”

The report is among the first detailed analyses to be released as the world waits for scientists to decipher the heavily mutated strain, first reported to the World Health Organization by South Africa on November 24.

However, the analysis is still an early attempt to understand the new variant, and it is missing key data on vaccinations and disease severity.

“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 authors wrote.

“Quantifying 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 are urgent priorities,” they said.

Co-author Anne von Gottberg, of the National Institute for Communicable Diseases, said that even as evidence from South Africa suggested previous infection may not protect people against reinfection with Omicron, there was hope it could still provide protection from severe disease, hospital admission and death.

It was also possible that the variant itself was not more transmissible than Delta, but that the population was just more susceptible, given the strain’s ability to reinfect, von Gottberg said at a WHO Africa media event on Thursday.

South Africa has seen a steep rise in daily cases in recent weeks – from only several hundred in mid-November to over 11,000 reported on Thursday. Around 75 per cent of the virus genomes sequenced for November so far have been Omicron, though the data is limited.

Findings in the new report are based on data collected between early March 2020 and November 27 this year through South Africa’s national surveillance system. Some 35,670 patients with reinfections out of nearly 3 million cumulative cases were considered in the study.

The scientists used modelling to evaluate the relative risk for reinfection in each of South Africa’s waves. People who had sequential positive tests at least 90 days apart were considered to have reinfections.

They found no increase in the relative risk of reinfection in waves following the spread of both the Beta and Delta variants, even as there was increased risk of a primary infection with these strains.

This time, the scientists observed a decreased risk of primary infection since October, which lead author Juliet Pulliam suggested on Twitter could be “partially explained by vaccine roll-out”. But data suggest an estimated threefold increase in the risk of reinfection during this period, according to a release from Stellenbosch University, where the South African Centre for Epidemiological Modelling and Analysis – which led the study – is based.

These included reinfections among people who tested positive during the recent Delta-dominated wave, which in South Africa peaked in July and ended in September.

Increasing vaccination uptake may reduce the risks of both primary infection and reinfection with Omicron, the researchers said. Around a quarter of South Africa’s population is fully vaccinated.

Virologist Jin Dong-Yan of the University of Hong Kong, who was not involved in the research, said that if the early findings on reinfection were accurate for South Africa, this would not necessarily indicate the trajectory of Omicron spread in other parts of the world, such as those with high vaccination rates.

“We need more data to understand the full picture,” Jin said, adding there was limited genetic sequencing to confirm the extent that new trends were driven by Omicron.

Michael Head, senior research fellow in global health at the University of Southampton in Britain, said the findings about immunity from previous infection made concerns about Omicron look “less and less” like a false alarm.

“However, the situation should, to some extent, be different with vaccine-generated immunity. The immune response from vaccination is much stronger when compared with infection-acquired immunity,” Head told Britain’s Science Media Centre.

The next few weeks would be an important period for confirming these early signals about reinfection, said the South African researchers, noting that their results could have been impacted by changes in testing or health-care behaviour throughout the pandemic.

Data about how well vaccines can impact the variant and more information about disease severity are expected in the coming days and weeks.