Scientists Are Racing to Find Out if Vaccines will Stop Omicron.

As nations severed air links from southern Africa amid fears of another global surge of the coronavirus, scientists scrambled on Sunday to gather data on the new Omicron variant, its capabilities and — perhaps most important — how effectively the current vaccines will protect against it.

The early findings are a mixed picture. The variant may be more transmissible and better able to evade the body’s immune responses, both to vaccination and to natural infection, than prior versions of the virus, experts said in interviews.

The vaccines may well continue to ward off severe illness and death, although booster doses may be needed to protect most people. Still, the makers of the two most effective vaccines, Pfizer-BioNTech and Moderna, are preparing to reformulate their shots if necessary.

“We really need to be vigilant about this new variant and preparing for it,” said Jesse Bloom, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle.

“Probably in a few weeks, we’ll have a better sense of how much this variant is spreading and how necessary it might be to push forward with a variant vaccine,” Dr. Bloom said.

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Already, Omicron accounts for most of the 2,300 new daily cases in the province of Gauteng, South Africa, President Cyril Ramaphosa announced on Sunday. Nationally, new infections have more than tripled in the past week, and test positivity has increased to 9 percent from 2 percent.

Scientists have reacted more quickly to Omicron than to any other variant. In just 36 hours from the first signs of trouble in South Africa on Tuesday, researchers analyzed samples from 100 infected patients, collated the data and alerted the world, said Tulio de Oliveira, a geneticist at the Nelson R. Mandela School of Medicine in Durban.

Within an hour of the first alarm, scientists in South Africa also rushed to test coronavirus vaccines against the new variant. Now, dozens of teams worldwide — including researchers at Pfizer-BioNTech and Moderna — have joined the chase. ...