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Data from South Africa suggests greater risk of reinfection by Omicron
Author: Media & Communication, Faculty of Science
Published: 02/12/2021

​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.

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 on 2 December 2021. Preprints are preliminary reports of work that has not been certified by peer review.

Prof Juliet Pulliam, director of the South African Centre for Epidemiological Modelling and Analysis (SACEMA) hosted at Stellenbosch University and first author, says they wanted to determine whether there is epidemiological evidence of increased risk of reinfection with the Omicron variant as compared to the Beta and Delta variants. 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.  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.

“In other words, 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," Prof Pulliam explains.

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.

According to Dr Harry Moultrie, senior medical epidemiologist in the Centre for Tuberculosis at the National Institute for Communicable Diseases (NICD), the findings have important implications for public health planning in countries such as South Africa and India with high rates of immunity from prior infections and low levels of vaccination uptake.

“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 says.

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

For the editors

  • The data were collected through South Africa's National Notifiable Medical Conditions Surveillance System and collated by researchers at the National Institute for Communicable Diseases (NICD).
  • The analysis is based on 2,796,982 individuals with laboratory-confirmed positive SARS-CoV-2 test results at least 90 days prior to 27 November 2021. Of these, 35,670 were suspected reinfections.
  • The data and code will be made available at and DOI: 10: 10.5281/zenodo.5745339

Media inquiries

Prof Juliet Pulliam

Director of the South African Centre for Epidemiological Modelling and Analysis (SACEMA) hosted at Stellenbosch University


For media interviews with Prof Pulliam, please arrange via whatsapp with Wiida Basson at 079 427 1976


Dr Harry Moultrie

Senior medical epidemiologist in the Centre for Tuberculosis at the National Institute for Communicable Diseases (NICD)


Mobile: 082 331 1618