(Photo: CDC)

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 say.

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

Within an hour of the first alarm, scientists in South Africa 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. They won’t know the results for two weeks, at the earliest. But the mutations that Omicron carries suggest that current vaccines most likely will be less effective, to some unknown degree, than against any previous variant.

Dr. Jesse Bloom at the Fred Hutchinson Cancer Research Center in the US, said Omicron mutations could make it more difficult for targeted immune proteins called antibodies to neutralize the virus.

South African doctors are seeing an increase in reinfections in people who already had a bout of COVID-19, suggesting that the variant can overcome natural immunity.

The Omicron variant has about 50 mutations, more than 30 of which are in the spike protein, the protein that all of the approved Covid-19 vaccines are designed to train human’s immune systems on.

Not all of the mutations are new. Some have been found in other variants. Others are thought to "inherit" the Beta variant's ability to avoid vaccines, while most are highly contagious like the Delta variant.