Omicron appears to evade immunity from prior Covid-19 infection, data shows

The Omicron variant appears to be able to evade immunity from prior Covid-19 infection, new data has suggested.

The South African Centre for Epidemiological Modelling and Analysis (SACEMA) and the National Centre for Communicable Diseases (NICD) released the data on Thursday night.

It also shows that there was a “three-fold increase in risk for reinfection” due to Omicron compared to previous variants.

In a press release, the SACEMA and NICD said that analysing data from March 4 2020 to November 27 2021 shows that the reinfection risk profile of Omicron was “substantially higher than that associated with the Beta and Delta variants during the second and third waves”.

This information is contained in a preprint article published on prepublication platform medrxiv.org on Thursday. Preprints are preliminary reports of work that have not been certified by peer review.

The article's author, SACEMA director Prof Juliet Pulliam, said that the authors wanted to determine whether there was epidemiological evidence of increased risk of reinfection with the Omicron variant compared to Beta and Delta.

“This is an important question, as an increase of reinfections rather than new infections would serve as an indication that the new variant has developed the ability to evade natural immunity from previous infection.

“Their findings show that the relative risk of reinfection has been stable during previous waves, but that this risk has increased three-fold between the beginning of October and the end of November. Though the relative risk of primary infection has increased with each subsequent wave (due to increased transmissibility and behaviour change), this does not seem to be the case for Omicron based on this preliminary data.

“The timing of this deviation in the epidemiological data is associated with the emergence of the Omicron variant, identified by South African scientists and announced to the public on November 25 2021,” the two organisations said in a joint release.

The authors of the articles say that while Gauteng is the epicentre of the fourth wave, similar patterns of increased infections were starting to emerge across SA.

“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,” they write in the article.

This information was crucial, said Dr Harry Moultrie, senior medical epidemiologist in the Centre for Tuberculosis at the National Institute for Communicable Diseases (NICD), in countries with high immunity from prior infection but with low vaccination uptake — particularly countries like SA and India.

“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.

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