Omicron variant infects around 70 times faster than Delta, researchers say

The Omicron variant infects around 70 times faster than the Delta and original Covid-19 strains, researchers have said, but the severity of the illness it causes is likely to be much lower.

A team at Hong Kong University said the newest variant of concern replicated less efficiently – a rate more than 10 times lower – in human lung tissue than the original strain.

Study leader Dr Michael Chan Chi-wai said it was too early to be definitive but that the findings of their yet to be published scientific paper may signal Omicron causes a “lower severity of disease” when compared to the Delta variant.

The study adds weight to initial on the ground observations by doctors in South Africa about severity of illness and provides further evidence that Omicron is more contagious than any previous variant of Covid-19.

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It suggests that Omicron multiplies much faster in people’s airways but far slower in the lungs, and that it transfers faster from one person to another.

“It is important to note that the severity of disease in humans is not determined only by virus replication,” Dr Chan Chi-wai said. “It is also determined by each person’s immune response to the infection, which sometimes evolves into life-threatening inflammation.

“By infecting many more people, a very infectious virus may cause more severe disease and death even though the virus itself may be less pathogenic.

“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.”

‘Impossible to contain’

In response, Dr Muge Cevik, an infectious-disease specialist at the University of St Andrews, Scotland, said much about Omicron remains uncertain but its infectiousness seems clear.

“The only thing I am sure of is that Omicron will spread so quickly through the population, making it likely impossible to contain even with the most stringent measures and giving us very little time over the next few weeks. So get your vaccines and boosters!” she said on Twitter.

The Hong Kong study used human tissue to look at virus replication in the lab; “so this is not a definitive but supportive finding and needs to be confirmed by clinical data as host immune response is absent in these studies”, she added.

It also explains why it spreads quickly and outcompeted Delta in South Africa, which fits with modelling assumptions on likely spread of the disease.

“There’s a lot we don’t yet understand about Omicron, including its impact on immunity and what it means for vaccines. New data will be emerging over the next few weeks which could be misinterpreted without context,” Dr Cevik added.

For those asking whether these findings were good or bad news, she said the simple answer was: “I don’t know. While Omicron may infect the lung cells less efficiently, a higher viral load may worsen immune response.”