By Dan Robitzski

Newly shared preliminary data suggests that the Omicron variant of SARS-CoV-2 may target and infect tissues within the respiratory tract at different rates than do the Delta variant and other predecessors. In fact, some experts say, the Omicron variant may owe its enhanced transmissibility to its facility for infecting bronchial tissue far more than the lungs.

Findings from the research, which hasn’t yet undergone peer review, were shared online in a University of Hong Kong news release on Wednesday (December 15). In lung tissue taken from a human patient, the researchers found that the Omicron variant replicated roughly 70 times more in the bronchial tissue that makes up tubes leading into the lungs than did the Delta variant after 24 hours. However, Omicron variant replicated more than 10 times slower in lung tissue than the original coronavirus variant. It’s difficult to extrapolate clinical outcomes from this type of lab-based research, but the researchers suggest in the news release that the fast bronchial replication could explain why the Omicron variant seems to be so highly infectious—spreading more than twice as quickly as Delta, according to a not-yet-peer reviewed analysis reported in The New York Times. Other variants’ greater presence deeper in the lungs could explain preliminary reports suggesting that Omicron cases tend to be more mild than those caused by other variants—although there are conflicting analyses on that point, and well as alternative explanations.

The finding “was not surprising to me, based on the preliminary data that’s discussed in these circles,” says University of Minnesota pediatrician and infectious disease expert Beth Thielen. “The rapidity with which Omicron has outcompeted Delta in South Africa—that suggests to me that it has a fitness advantage.”

READ MORE