Pfizer has started making a vaccine against the omicron Covid variant, its chief executive confirmed on Monday.
Albert Bourla said the first DNA template for the new jab was completed on Friday and predicted it would be ready to roll out by early next year.
"Within 95 days, basically we will have a new vaccine," he told the US business news channel CNBC. "Already, we started on Friday.
"Friday, we made our first DNA template which is the first part of the manufacturing, of the development process of a new vaccine, and we have made clear that we will be able to have a vaccine in less than 100 days.
"In fact, we have already two vaccines built in less than 100 days. We built one for delta that we did not use because the current vaccine is very effective against delta.
"We built one for beta, which also we didn't have to use, so we will build one for omicron that will be used only in case we need it if we see that the current one doesn't work."
However, Mr Bourla said a new vaccine may not be needed because he believed the current jabs would still be effective.
Although the delta variant proved more infectious for vaccinated people, it did not raise the risk of serious illness or death.
Pfizer also plans to trial its delta and beta vaccines against omicron to see whether they work better than the current jabs, based on the original "wild type" virus. A new vaccine could be available by late February under the current timelines.
"I don't think that the result will be that the vaccines don't protect," added Mr Bourla. "I don't know if it will be equally effective at 95 plus per cent against the omicron. But I will be very surprised if we are very, very, very low."
Paul Burton, the Moderna chief medical officer, also said a reformulated vaccine against omicron could be rolled out next year. The vaccine maker "mobilised hundreds" of workers on Thursday to start studying the new variant, he said.
AstraZeneca said its platform could respond quickly to new variants and the company had also begun testing its antibody cocktail against the new variant.