Highlighting growing concerns over Omicron, scientists in South Africa said on Friday that the latest variant of the coronavirus appears 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 & Tropical Medicine who led the analysis. “It is possible that it is even less transmissible than Delta.”

Some of these researchers had reported Thursday that the new variant could partly bypass immunity acquired from a previous infection. It is still unclear whether, or to what extent, Omicron may escape the protection afforded by current vaccines.

The new research was posted on Twitter, and has not yet been peer reviewed or published in a scientific journal.

The Omicron variant has appeared in nearly two dozen countries. The United States has identified at least 10 cases in six states, and health officials say community spread of the virus is inevitable. President Biden reiterated on Friday morning that his administration’s latest pandemic measures, announced earlier 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 the 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 previous research. on immunity.

Omicron cases in particular are doubling about every three days in Gauteng province, home to the densely populated economic center of South Africa and now the epicenter of the country’s fourth wave of infections, the people said on Friday. researchers.

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 that of Delta.

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. In related 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 did not last as long as it did. ‘she did it. The increase in re-infections has coincided with the spread of Omicron in the country.

The team did not confirm that the observed re-infections were due to the 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.

The increase in cases in South Africa has been accompanied by a week-over-week increase in hospital admissions, already higher than in previous waves, according to data from the South National Institute – African communicable diseases.

But it’s not yet clear whether Omicron causes more serious illness than other versions of the coronavirus. The percentage of new cases found in children under 5 has also risen sharply in the country, but this may be because more adults are now being vaccinated.