Highlighting growing concern about Omicron, South African scientists said Friday that the newest variant of the coronavirus appears to be spreading more than twice as fast as Delta, which was considered the most contagious version of the virus.
The rapid spread of Omicron is the result of a combination of infectiousness and the ability to evade the body’s immune defenses, the researchers said. But the contribution of each factor has not yet been determined.
“We’re not sure what this mixture is,” said Carl Pearson, a mathematical modeling developer at the London School of Hygiene and Tropical Medicine who led the analysis. “It is possible that it may even be less contagious than Delta.”
Dr. Pearson posted the results on Twitter… The study has not yet been peer-reviewed or published in scientific journals.
Researchers said Thursday that the new variant could partially escape the immunity it received from a previous infection. It is still unclear if Omicron can avoid the protection provided by vaccines, and to what extent.
But some experts said they expect a similar result.
“It’s scary that there are so many re-infections, which means that the immunity induced by the vaccine could be affected in a similar way,” said Akiko Iwasaki, an immunologist at Yale University.
The Omicron variant has appeared in almost two dozen countries. In the United States, at least 10 cases have been identified in six states. President Biden confirmed Friday morning that his administration’s latest pandemic response, announced this week, should be sufficient to contain the spread of Omicron.
This variant was first identified in South Africa on 23 November and quickly caused about three quarters of new cases in that country. South Africa reported 11,535 new coronavirus cases Thursday, up 35 percent from the day before, and test positive increased to 22.4 percent from 16.5 percent.
“It’s actually really amazing how quickly it seemed to take over,” said Juliet Pulliam, director of the Center for Epidemiological Modeling at the University of Stellenbosch in South Africa, which led earlier research on immunity.
The number of Omicron cases doubles roughly every three days in Gauteng province, home to South Africa’s densely populated economic center, according to new estimates from researchers.
In the course of mathematical analysis, they estimated the Rt of the variant – an indicator of the speed of the spread of the virus – and compared it with the metric for Delta. They found that the Omicron’s Rt is almost 2.5 times that of the Delta.
This figure depends not only on how contagious the variant might be, but also on its ability to bypass the body’s immune defenses when it reaches a new host.
December 3, 2021 5:44 PM ET
Based on the mutations carried by Omicron, some researchers have warned that this variant may be highly transmissible and that current vaccines may not be as effective against it as against previous variants.
In a study published Thursday, Dr. Pulliam and her colleagues evaluated the new variant’s ability to evade immunity by examining confirmed cases in the country through the end of November.
They reported an increase in reinfections among people who tested positive for the virus at least 90 days ago, suggesting that the immunity gained from a previous fight with the virus was no longer as protective as it seemed. The rise in re-infections has coincided with the spread of Omicron throughout the country.
According to Dr. Pulliam, a feature of Omicron’s genetic code made it easy to distinguish this variant from Delta in diagnostic tests, and this helped scientists to quickly detect its sharp growth.
“If we didn’t have that, we would probably be several weeks behind where we are now in terms of recognizing a new option,” she added.
The team did not confirm that the re-infections they observed were due to the new variant, but said it was a reasonable assumption. Scientists noted that there was no such surge when the Beta and Delta variants dominated.
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Dr Pulliam and her colleagues estimate that the risk of re-infection with the Omicron variant is about 2.4 times higher than the risk seen with the original coronavirus.
Vaccines are thought to produce much higher levels of antibodies in the body compared to levels resulting from infection with the coronavirus. But antibodies produced after infection are capable of warding off variants with a wider range of mutations, said Florian Krammer, an immunologist at Icahn School of Medicine on Mount Sinai in New York.
If a new variant re-infects people who have recovered from Covid, “I don’t think there will be much difference” in how Omicron will respond to vaccines, Dr. Krammer said. “This is a bad sign.”
South African researchers did not have information on the severity of the first disease compared to the second. But the immune system must be able to prevent the most severe symptoms in people who have previously been infected or have been immunized, Dr. Iwasaki said.
“I suspect and hope that not all of this will lead to serious illness,” she said. “There may be many infections, but they may be more mild.”
South Africa’s Gauteng province is currently the epicenter of the country’s fourth wave of infections, according to scientists. The weekly increase in hospital admissions is already higher than in previous waves, according to the National Institute of Infectious Diseases of South Africa.
“Gauteng was completely hit by the Delta wave just five months ago, so there is no doubt that this option is causing a significant number of re-infections just because of this fact,” said Christian Andersen, a virologist at the Scripps Research Institute in San Diego.
The proportion of children under 5 years of age among the total number of cases has also increased sharply (second only to children over 60), but this may be due to the fact that more adults are now immunized than in previous waves.
Pediatricians also admit more children to hospitals, but mostly as a precautionary measure, ”said Dr. Vaasila Jassat, a public health specialist at the National Institute for Infectious Diseases.
“Later in the wave, they will not meet the eligibility criteria,” said Dr. Jassat. According to her, most of the hospitalized children are not vaccinated and live with their parents who were also not vaccinated.
Linsey Chutel provided a reportage from South Africa.