A woman getting tested for COVID-19 at a mobile testing site at Times Square in New York City on Dec 6, 2021Share on Pinterest
A woman getting tested for COVID-19 at a mobile testing site at Times Square in New York City on December 6, 2021. Anadolu Agency/Getty Images
  • Omicron, which is the latest SARS-CoV-2 variant of concern, is spreading globally.
  • A South African study has found high rates of reinfection among those with previous confirmed SARS-CoV-2 infections since the beginning of November. This was when scientists discovered the Omicron variant there.
  • These observations suggest that Omicron can evade immunity from prior infection.

All data and statistics are based on publicly available data at the time of publication. Some information may be out of date. Visit our coronavirus hub for the most recent information on the COVID-19 pandemic.

A preprint study from South Africa suggests that the Omicron variant of SARS-CoV-2 is more than three times as likely to reinfect people than previous variants.

This ability to evade immunity from prior infection may be causing its rapid spread.

For the study, which has not yet undergone peer review, researchers rapidly analyzed 2,796,982 confirmed SARS-CoV-2 cases in South Africa. All first infections had occurred at least 90 days before November 27, 2021.

The researchers identified primary infections and suspected repeat infections. They considered anyone who tested positive again more than 90 days after their first positive test to have a reinfection with SARS-CoV-2.

The team analyzed whether or not there were differences in reinfection risk during the first, second, and third waves. The second wave was dominated by the Beta variant, the third wave was dominated by the Delta variant, and experts assume that the Omicron variant has dominated reinfections since November 2021.

They judged a higher relative risk of reinfection among the population in any wave as indicating immune escape by the virus. Immune escape means that the virus can evade immunity acquired through either infection or vaccination.

Of the sample, 35,670 people (1.3%) had two confirmed SARS-CoV-2 infections. There were peaks of reinfection in January and July 2021, which corresponded with the peak of waves two and three in South Africa, along with a spike in reinfections in November 2021, which corresponded with the detection of the Omicron variant there.

The researchers suggest that this means that Omicron can evade prior immunity. They call for in vitro studies to test this.

They also note that although in vitro studies for the Beta and Delta variants suggested that they could evade prior immunity more effectively than the original Alpha variant, their own analysis did not show this at a population level. This is because there was no increased risk of reinfection in either the second or third waves compared with the first.

The authors suggest that scientists need to design better experiments to determine the risk of immune escape in vitro.

Dr. Chris Coleman — an assistant professor of infection immunology at the University of Nottingham in the United Kingdom — told Medical News Today: “This is a clear sign that the new variant is escaping immune responses, as this is evading the ‘natural’ response — which may be more complex than vaccine-induced response.”

For more advice on COVID-19 prevention and treatment, visit our coronavirus hub.

These findings may have implications for public health planning. For example, if Omicron is more transmissible and can evade immunity, the potential for spread is enormous. The authors question whether or not immune escape will mean that people are less protected against severe COVID-19.

Experts have noted that most Omicron infections have, so far, led to only mild symptoms, and there have been no recorded deaths yet. However, the ability of Omicron to reinfect is worrying.

Dr. Arturo Casadevall, Ph.D. — chair of the Molecular Microbiology & Immunology Department at Johns Hopkins Bloomberg School of Public Health in Baltimore — highlighted that concern.

He said: “These results imply that Omicron has changed so much relative to the other variants that prior COVID-19 immunity is not as protective. This finding is very concerning because it implies that whatever immunity was built up by prior COVID-19 is not sufficient to protect against Omicron.”

In speaking to the Science Media Centre, Prof. Paul Hunter — a professor of medicine at the Norwich School of Medicine in the U.K. — agreed.

“Unlike previous waves that were because the variants were intrinsically more infectious, Omicron appears to […] have substantial immune escape, at least from immunity caused by a natural infection. Whether Omicron is also more infectious is possible but cannot be answered by this analysis.”

– Prof. Paul Hunter

The authors point out that their study cannot answer the question about whether or not the current vaccines will be effective against Omicron. At the time of the study, vaccination levels in South Africa were very low.

However, experts believe that — as with other variants — even if vaccines do not prevent infection, they should prevent severe COVID-19 from Omicron.

The vaccination status of those with suspected reinfections in this study was not known.

“One key question, of course, is if this [increased risk of reinfection with Omicron] also applies to vaccinated individuals and, as they say, the public health implications (e.g., is the infection milder with reinfection?).”

– Dr. Chris Coleman

Dr. Casadevall stressed: “These findings heighten the concern that the same [immune escape] may happen in those vaccinated. Omicron is showing itself to be a very dangerous new variant with the potential to set back some of the progress we have made against COVID-19.”

So, until we have more data about Omicron, experts are clear that the priority is to get as many people vaccinated as possible.

Dr. Michael Head, Ph.D. — a senior research fellow in global health at the University of Southampton in the U.K. — told the Science Media Centre: “[While] we await more data to emerge over the coming days and weeks, the message to the general public has to be — go and get all the doses you are eligible for.”

For live updates on the latest developments regarding the novel coronavirus and COVID-19, click here.