NPR reports: In late November, more than 110 people gathered at a crowded Christmas party at a restaurant in Oslo. 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 super spreader 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. […] The variant’s many mutations on the spike protein allow it to infect human cells more efficiently than previous variants could, leaving many more people again vulnerable. Because of that, “immune escape” alone could be the major reason why the variant looks so contagious compared to delta, which was already highly transmissible.
In fact, omicron has been spreading at a pace that’s comparable to how fast the original strain of the coronavirus spread at the very beginning of the pandemic despite the world’s newfound levels of immunity. “The playing field for the virus right now is quite different than it was in the early days,” says Dr. Joshua Schiffer, an infectious disease researcher at Fred Hutchinson Cancer Research Center. “The majority of variants we’ve seen to date couldn’t survive in this immune environment.” Even delta was essentially at a “tie,” he says, where it was persisting, but “not growing very rapidly or decreasing very rapidly.” A new study from Denmark suggests that much of the variant’s dominance comes down to its ability to evade the body’s immune defenses. Researchers compared the spread of omicron and delta among members of the same household and concluded that omicron is about 2.7 to 3.7 times more infectious than the delta variant among vaccinated and boosted individuals.
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