The Omicron variant of COVID-19 multiplies roughly 70 times faster than the Delta but could lead to less severe infections because of its slow growth in the lungs, researchers found.
A University of Hong Kong study released Wednesday found the much faster rate of replication in the human bronchus — two tubes from the windpipe to the lungs — began at about 24 hours post-infection.
“In contrast, the Omicron variant replicated less efficiently (more than 10 times lower) in the human lung tissue than the original SARS-CoV-2 virus, which may suggest lower severity of disease,” according to the study.
The team of researchers led by Dr. Michael Chan Chi-wai said the findings could explain why Omicron may transmit faster between humans than previous strains despite its lower likelihood of leading to severe illness or death. The research is being peer-reviewed.
“It is also noted that, by infecting more people, a very infectious virus may cause more severe disease and death even though the virus itself may be less pathogenic,” Chan Chi-wai said.
Still, Chan warned not to dismiss the Omicron variant as a lesser risk as the data suggested it spreads faster but doesn’t appear to damage lung tissue as severely.
“Therefore, taken together with our recent studies showing that the Omicron variant can partially escape immunity from vaccines and past infection, the overall threat from Omicron variant is likely to be very significant,” Chan Chi-wai said.
Jeremy Kamil, an associate professor of microbiology and immunology at Louisiana State University Health Shreveport, told the Guardian the study shows Omicron replicates “fantastically well” — far better than Delta or the original virus — in bronchial tissue.
“This could in some ways contribute to an advantage in spread/transmission between people,” Kamil said. “Of course, a huge component of Omicron’s transmissibility in real life is going to be its potential to escape neutralizing antibodies that protect against infection in the first place.”
Kamil said Omicron — which is spreading at an unprecedented rate globally, according to the World Health Organization — is “very likely” spreading efficiently among vaccinated people, especially those who have not received a booster shot.
The new variant, which was first detected last month in South Africa, has raised concern among health experts as being more resistant to vaccines than earlier strains. It’s been confirmed in at least 77 nations as of Tuesday, although the head of WHO warned it’s probably spreading in “most countries” around the globe.
More than 5.3 people million worldwide, including more than 802,000 in the US, have died from COVID-19 as of Thursday, according to Johns Hopkins University data.