South African scientists have found an early signal of an increased risk of reinfection associated with the Omicron variant of SARS-CoV-2, thereby providing epidemiological evidence for the new variant’s ability to evade immunity from prior infection.

Main points:

· Epidemiological data from South Africa show three-fold increase in risk for reinfection due to Omicron, compared to previous variants.

· This finding provides epidemiological evidence for Omicron’s ability to evade immunity from prior infection.

· Next steps include quantifying the extent of Omicron’s immune escape for both natural and vaccine-derived immunity, as well as its transmissibility relative to other variants.

Data from South Africa suggests greater risk of reinfection by Omicron:

An analysis of routine surveillance data from South Africa from 4 March 2020 to 27 November 2021 show that the reinfection risk profile of Omicron is substantially higher than that associated with the Beta and Delta variants during the second and third waves, with observed numbers of reinfections falling well beyond the prediction intervals.

A preprint of the article, “Increased risk of SARS-CoV-2 reinfection associated with emergence of the Omicron variant in South Africa”, was published on the pre-publication platform medrxiv.org on 2 December 2021. Preprints are preliminary reports of work that has not been certified by peer review.

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. Although 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 25 November 2021.

While Gauteng is already experiencing the fourth wave, driven by the Omicron variant, it seems that a similar pattern may be emerging in other provinces: “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.

The 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.

In the meantime – whether you have had COVID previously or not –vaccination likely remains the best tool for protection against severe disease.