Omicron is highly transmissible. Scientists are looking for clues as to why

In late November 2021, more than 110 people gathered at a crowded Christmas party at a restaurant in Oslo, Norway. Most of the guests were fully vaccinated. One had returned from South Africa just a few days earlier and was unknowingly carrying the omicron variant of SARS-CoV-2. Ultimately, about 70% of the partygoers were infected. Scientists who traced this superspreader event concluded it was evidence that omicron was “highly transmissible” among fully vaccinated adults.

 

Just over a month later, omicron’s speedy worldwide ascent now makes it abundantly clear that the party wasn’t an isolated example. In country after country, the new variant has outcompeted its predecessor, the delta variant, with one case of omicron sparking at least three other new infections on average. Cases have soared to record highs in parts of Europe and now the U.S., where about half a million new infections have been recorded in a single day. “This is a game-changing virus, especially in the vaccinated population where people have had a level of invincibility,” says Sumit Chanda, a professor in the Department of Immunology and Microbiology at Scripps Research.

 
 

Indeed, in a world where vaccinations and infections have built up immunity, other variants were having trouble gaining a foothold. Yet omicron is thriving. “This changes the calculus for everybody,” says Chanda. And so scientists are trying to figure out: What accounts for omicron’s lightning-quick spread? While it’s still early, they’re starting to piece together why the new variant is so contagious — and whether that means old assumptions about how to stay safe need to be revamped.

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