Together with its ability to escape vax immunity, variant’s threat high: Study

In the first findings on how the hypermutated Omicron variant infects the respiratory tract, researchers from Hong Kong University (HKU) on Thursday reported that the virus multiplies 70 times faster in the bronchi than Delta and the original SARS-CoV-2 virus, which, they said, might explain why Omicron transmits faster.

The researchers said Omicron infection may be less severe, depending on the body’s immune response. The variant reaches higher levels in the tissue, compared to Delta, 48 hours after infection, said the study.

The preliminary data, published online on Wednesday, gives for the first time a look at how Omicron may behave inside the respiratory tract — and the data offers a tantalising clue as to why this heavily mutated variant is spreading so fast and even outcompeting Delta.

Michael Chan Chi-wai, who led the work, said the result needed to be interpreted with caution because the severe disease is determined not only by how quickly the virus replicates but also by a person’s immune response and, in particular, whether the immune system goes into overdrive, causing a so-called cytokine storm.

“It is also noted that 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,” he said. “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 the Omicron variant is likely to be very significant.”

Jeremy Kamil, an Associate Professor of microbiology and immunology at Louisiana State University Health Shreveport, pointed out that Delta, which turned out to be more pathogenic, showed a similar pattern of replicating more slowly in the lungs.

“These authors found Omicron replicates fantastically well — even far better than either Delta or the original virus — in bronchial tissue,” Kamil said. “This could in some ways contribute to an advantage in spread/transmission between people.

“Of course, a huge component of Omicron’s transmissibility in real life is going to be its potential to escape neutralising antibodies that protect against infection in the first place. It’s very likely spreading well even between vaccinated people, especially those who haven’t recently gotten a booster shot.”

The initial data, published online and not yet peer-reviewed, came from experiments using lung tissue samples taken from patients during surgery. By 24 hours, the Omicron variant had replicated about 70 times more than Delta and the original variant. Although the bronchus is not the upper respiratory system, scientists said this could lead to people shedding more virus and passing on infections more easily.

The findings, together with other recent work showing Omicron infects cells more readily, add to an emerging picture that the variant may be intrinsically more transmissible in addition to evading existing immunity.

Tedros Adhanom Ghebreyesus, Director-General of WHO, has already pointed out that “seventy-seven countries have now reported cases of Omicron, and the reality is that Omicron is probably in most countries, even if it hasn’t been detected yet. Omicron is spreading at a rate we have not seen with any previous variant.”

The European Centre for Disease Prevention and Control (ECDC) said modeling projections of the HK study point to an imminent rapid spread of Omicron and that it will probably be the dominant variant in the first 2 months of 2022.

Echoing what the HKU lung tissue researchers said, the ECDC said even if the severity is the same as or lower than Delta, exponential Omicron growth could outweigh any of those benefits. It said the threat of further spread and its impact on public health are very high.