Omicron variant spreads twice as fast as Delta in South Africa


Highlighting growing concerns over Omicron, scientists in South Africa said on Friday that the latest variant of the coronavirus appeared to be spreading more than twice as fast as Delta, which had been considered the most contagious version of the virus.

Omicron’s rapid spread is the result of a combination of contagiousness and an ability to dodge the body’s immune defenses, the researchers said. But the contribution of each factor is not yet certain.

“We don’t know what that mixture is,” said Carl Pearson, a mathematical modeler at the London School of Hygiene and Tropical Medicine who led the analysis. “It is possible that it is even less transmissible than Delta.”

Dr Pearson posted the results on Twitter. The research has not yet been peer reviewed or published in a scientific journal.

On Thursday, researchers reported that the new variant could in part bypass immunity gained from a previous infection. It is still not clear whether, or to what extent, Omicron may escape the protection conferred by vaccines.

But some experts have said they would expect the outcome to be similar.

“It’s scary that there are so many re-infections, which means that vaccine-induced immunity can also be affected in the same way,” said Akiko Iwasaki, immunologist at Yale.

The Omicron variant has appeared in nearly two dozen countries. The United States has identified at least 10 cases in six states. President Biden reiterated on Friday morning that his administration’s latest pandemic measures, which were announced this week, should be enough to mitigate the spread of Omicron.

The variant was first identified in South Africa on November 23 and quickly became responsible for around three-quarters of new cases in that country. South Africa reported 11,535 new coronavirus cases on Thursday, a 35% jump from the previous day, and the proportion of positive test results increased to 22.4 percent by 16.5 percent.

“It’s actually really striking how quickly it seems to have taken hold,” said Juliet Pulliam, director of an epidemiological modeling center at Stellenbosch University in South Africa, who led the initial research. on immunity.

Omicron cases are doubling about every three days in Gauteng province, home to the densely populated economic center of South Africa, researchers’ new estimates show.

In a mathematical analysis, they estimated the Rt of the variant – a measure of how quickly a virus spreads – and compared it to Delta’s metric. They found that Omicron’s Rt is nearly 2.5 times higher than Delta’s.

This number depends not only on the contagiousness of the variant, but also on its ability to bypass the body’s immune defenses once it reaches a new host.

Based on the mutations that Omicron carries, some researchers had warned that the variant could turn out to be highly transmissible, and that current vaccines may not be as effective against it as against previous variants.

In research published Thursday, Dr Pulliam and his colleagues estimated the ability of the new variant to evade immunity by examining confirmed cases in the country through the end of November.

They reported an increase in re-infections among people who had tested positive for the virus at least 90 days earlier, suggesting that the immunity gained from a previous bout with the virus was no longer as protective as it was. she had appeared. The increase in re-infections has coincided with the spread of Omicron in the country.

A quirk in Omicron’s genetic code made it easy to distinguish the Delta variant in diagnostic tests, and this helped scientists quickly spot its sharp rise, Dr Pulliam said.

“If we hadn’t had this, we would probably be several weeks behind what we have now in terms of recognizing the existence of a new variant,” she added.

The team did not confirm that the observed re-infections were caused by the new variant, but said it was a reasonable assumption. A similar peak did not occur when the beta and delta variants were dominant, the scientists noted.

Dr Pulliam and his colleagues estimated that the risk of re-infection with the Omicron variant is about 2.4 times the risk seen with the original version of the coronavirus.

Vaccines are believed to produce much higher levels of antibodies in the body, compared to the levels produced by infection with the coronavirus. But antibodies produced after infection are able to fend off variants with a wider range of mutations, noted Florian Krammer, an immunologist at Icahn School of Medicine at Mount Sinai in New York City.

If the new variant re-infects people who have recovered from Covid, “I don’t think there will be much difference” in how Omicron responds to vaccines, Dr Krammer said. “It is not a good sign.”

South African researchers did not have information on the severity of the first disease compared to the second. But the immune system should be able to prevent more severe symptoms in people who have had an infection or have been immunized, Dr Iwasaki said.

“I suspect, and I hope all of this is not going to lead to serious illness,” she said. “Maybe there are a lot of infections, but they can be milder.”

South Africa’s Gauteng province is now the epicenter of what scientists say is the country’s fourth wave of infections. The week-over-week increase in hospital admissions is already higher than in previous waves, according to data from South Africa’s National Institute of Communicable Diseases.

“Gauteng was absolutely crushed by the Delta wave only five months ago, so there is no doubt that this variant is causing a significant number of re-infections just for this fact,” said Kristian Andersen. , virologist at the Scripps Research Institute in San Diego.

The percentage of children under 5 among the total number of cases has also increased sharply – just behind those over 60 – but this may be because more adults are being vaccinated now than in previous waves. .

Pediatricians are also admitting more children to hospitals, but mainly as a precaution, said Dr Waasila Jassat, a public health specialist at the National Institute of Communicable Diseases.

“Later in the wave, they would not meet the admission criteria,” Dr Jassat said. Most children in hospital are not vaccinated, she said, and live with parents who have not been vaccinated either.

Lynsey chutel contributed reporting from South Africa.

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