Omicron now spreading twice as fast as delta in South Africa
Underscoring growing concerns about omicron, scientists in South Africa said Friday that the newest coronavirus variant appears to spread more than twice as quickly as delta, which had been considered the most contagious version of the virus.
Omicron’s rapid spread results from 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’re not sure what that mixture is,” said Carl Pearson, a mathematical modeler at the London School of Hygiene & Tropical Medicine who led the analysis. “It’s possible that it might even be less transmissible than delta.”
Some of these researchers had reported Thursday that the new variant may partly dodge immunity gained from a previous infection.
It’s still unclear whether, or to what degree, omicron may evade protection conferred by the 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The new research was posted on Twitter and has not yet been peer-reviewed or published in a scientific journal.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 since it was first identified in South Africa on Nov. 23 and has quickly come to account for about three-quarters of new cases in the country. South Africa reported 11,535 new coronavirus cases Thursday, a 35 percent jump from the day before, and the proportion of positive test results increased to 22.4 percent from 16.5 percent.
“It is actually really striking how quickly it seems to have taken over,” said Juliet Pulliam, director of an epidemiological modeling center at the University of Stellenbosch in South Africa, who led the earlier research on immunity.
Omicron cases in particular are doubling roughly every three days in Gauteng province, home to South Africa’s densely populated economic hub and now the epicenter of the country’s fourth wave of infections, the researchers said Friday.
In a mathematical analysis, they estimated the variant’s Rt — a measure of how quickly a virus spreads — and compared it with the metric for delta. They found that omicron’s Rt is nearly 2.5 times higher than that of delta.
That figure depends on not just how contagious the variant may be but also on its ability to sidestep the body’s immune defenses once it reaches a new host.