Omicron spread about 70 times quicker than Delta in human bronchial samples, a lab study found

• New data from a lab study could help explain why Omicron is spreading so quickly.
• It replicated 70 times faster than Delta in the bronchus, tubes between the windpipe and lungs.

The Omicron virus variant spread 70 times quicker than Delta in lab samples of tissue from the human airway, a study found.

The findings, shared by the University of Hong Kong in a press release Wednesday, could provide clues as to why the variant is spreading so quickly.

The detail of the findings has not been published or peer-reviewed.

In the lab, scientists applied Omicron, Delta, or the "original" variant of the coronavirus to tissue taken from two parts of the human respiratory system: the lungs and also the bronchus, tubes that connect the lungs to the windpipe.

Twenty-four hours later, Omicron was found to have replicated about 70 times faster in bronchus tissue than the Delta variant, and around 70 times faster than the "original" variant.

That "may explain" why Omicron seems to be spreading faster than previous variants, the authors of the study said in the press release.

By contrast, Omicron spread 10 times slower in lung tissue than the original strain. It also spread slower than Delta, although from the press release alone it was not clear by how much.

That could "suggest lower severity of disease," per the press release.

Is Omicron more infectious but milder? The jury is still out

The authors of the Hong Kong study stressed that these lab results give only an indication of how Omicron could behave in living people.

"It is important to note that the severity of disease in humans is not determined only by virus replication but also by the host immune response to the infection," said Michael Chan Chi-wai, lead author on the study.

Still, the findings are in line with reports from the European Medicines Agency and US CDC that, so far, Omicron seems to be spreading faster but cases have been mostly mild.

However, deaths and hospitalizations have also been reported after Omicron. Even a less severe virus can seriously harm and kill many people if it spreads across vast populations.

The World Health Organization has warned that it is still too early to conclude that Omicron is "milder" than other variants.

"We're concerned that people are dismissing Omicron as mild. Surely we have learned by now that we underestimate this virus at our peril," WHO leader Tedros Adhanom Ghebreyesus said Tuesday.

Whether Omicron will cause more virus in the upper airways but less virus in the lungs, and whether that will then translate into less severe disease, remains to be seen.

Muge Cevik, an infectious diseases expert at the University of St. Andrews in Edinburgh, Scotland, argued in a Twitter thread Wednesday that much remains unknown.

"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 & giving us very little time over the next few weeks. So get your vaccines & boosters!" she said.