Moderna CEO Stephane Bancel on Monday said it will take months to develop and ship a vaccine that specifically targets the omicron variant of the virus that causes Covid-19.

However, a higher 100-microgram dose of the company’s booster shot could be ready much sooner.

“The higher dose could be done right away but it will be months before the omicron specific variant is ready to ship in massive quantities,” Bancel told CNBC’s “Squawk Box.”

Bancel said Moderna believes the omicron variant is highly infectious, but it will take at least two weeks determine how much the mutations have impacted the efficacy of the vaccines currently on the market.

“Depending on how much it dropped, we might decide on the one hand to give a higher dose of the current vaccine around the world to protect people, maybe people at very high risk, the immunocomprised, and the elderly should need a fourth dose” he said.

Dr. Scott Gottlieb, former commissioner of the Food and Drug Administration, told CNBC that the FDA can move “very quickly” to approve a new vaccine to target omicron.

“I think the FDA is in a position to move very quickly at this point because they understand the basic platform, the manufacturing has been inspected, they understand the risk-benefit of the mRNA platforms generally,” said Gottlieb, who is a Pfizer board member.

Pfizer CEO Albert Bourla said the impact of omicron on the company’s two-dose vaccine remains to be seen.

“I don’t think that the result will be the vaccines don’t protect,” Bourla said. “I think the result could be, which we don’t know yet, the vaccines protect less.”

Bourla said Pfizer has already begun work to manufacture a new vaccine if necessary. The company made its first DNA template on Friday, he said, the first step in the development process.

“We have made multiple times clear that we would be able to have vaccine in less than 100 days,” Bourla said. He noted that the company was able to create vaccines for the beta and delta variants quickly, though they ultimately weren’t used because the original shots remained effective.

The World Health Organization, in a technical paper published Sunday, said omicron has more than 30 mutations on the spike protein that binds to human cells. These mutations are associated with higher transmission and potentially reduced antibody protection, according to the paper.

Omicron was first identified in South Africa’s Gauteng province where Johannesburg is located. Bancel warned that the variant is spreading globally already. He pointed to flights that arrived in Amsterdam from South Africa on Friday in which 61 of 624 passengers tested positive for Covid. At least 13 of them are infected with the omicron strain as health authorities continue to sequence the samples, according to the Dutch National Institute for Public Health.

“We also believe it is already present in most countries,” Bancel said. “I believe most countries that have direct flights from South Africa in the last seven to 10 days already have cases in their country that they may not be aware of.”

The U.S. has banned entry to non-citizens who have traveled in South Africa and seven other nations in the region in the past 14 days. The United Kingdom and the European Union have implemented similar travel restrictions.

The U.S. Centers for Disease Control and Prevention said on Friday that a case has not yet been identified in the U.S. However, White House chief medical advisor Dr. Anthony Fauci said on Sunday the variant will inevitably arrive in the U.S. Two cases of omicron have been identified in Ontario, Canada, according to the country’s public health agency.

Fauci told ABC’s “This Week” that it’s too early to say whether new mandates or lockdowns will be necessary to fight the variant. Dr. Angelique Coetzee, chair of the South African Medical Association, described the symptoms linked to omicron as “extremely mild” so far. “

However, Bancel warned that the symptoms reported in South Africa may not be a good predictor of the variant’s virulence since less than 5% of the population is over 60 and has far fewer comorbidities than the U.S. and Europe, which tend to have older and sicker citizens.

“I think today, it’s really impossible to know … I don’t believe that what’s going to happen in the coming week or two in South Africa will be predicting to be full virulence of a virus,” he said.

The variant has spooked global markets, with the Dow Jones Industrial Average dropping 905 points on Friday or 2.53%, it’s worst day of the year.