Vaccine efficacy for the “highly contagious” Omicron variant has likely dropped — but the full data won’t be available for at least two weeks, Moderna CEO Stephane Bancel warned on Monday.

“We need to wait for the data to see if it’s true and how much it is going down,” the drugmaker boss told CNBC’s “Squawk Box.”

Omicron already appears to be “much more infectious” than the Delta variant and is on track to become the most dominant strain in southern Africa in a matter of weeks, according to Bancel.

“It took four months for Delta variant to overtake Beta variant. Omicron is overtaking Delta in South Africa in a few weeks,” he said.

“We believe this virus is highly contagious. We need to get more data to confirm this but it seems to be much more infectious than Delta, which is problematic.”

Bancel added, “[There is] a lot of mutations in the spike protein, which is important for the vaccine. I don’t believe many people would have predicted such a big jump in evolution in one variant.”

The drugmaker predicted that the majority of countries with direct flights from southern Africa within the last seven to 10 days would already have Omicron cases — even if they haven’t been detected yet.

He added that the measures taken by some countries, including the US, to ban flights from the eight countries in that region could “slow down the progress of the virus while we figure out the efficacy of the vaccine.”

“I think those actions can save a lot of lives down the road,” Bancel said.

Over the weekend, the list of countries that have spotted the new variant in travelers grew and the World Health Organization labeled it a “variant of concern,” which is the most serious designation of a COVID-19 variant.

Health authorities are rushing to determine if the Omicron variant is more transmissible — or if infection causes more serious illness — than other strains.

The variant appears to have a high number of mutations — about 30 — in the coronavirus’ spike protein, which could affect how easily it spreads to people.

Some experts have already said that could mean that vaccine makers may have to adapt their products at some point.

Bancel estimated Monday it could take 60 to 90 days for an Omicon-specific vaccine to be tweaked and approved by drug regulators.