The University of Oxford on Tuesday said there was no evidence that vaccines would not prevent severe disease from Omicron, but that it was ready to rapidly develop an updated version of its vaccine developed with AstraZeneca if necessary.

Earlier on Tuesday, the head of drugmaker Moderna said that Covid-19 shots were unlikely to be as effective against the variant, jolting global markets.

The University of Oxford said that there was limited data on Omicron so far and that it would carefully evaluate the impact of the variant on its shot, echoing an AstraZeneca statement last week.

"Despite the appearance of new variants over the past year, vaccines have continued to provide very high levels of protection against severe disease and there is no evidence so far that Omicron is any different," it said in a statement.

"However, we have the necessary tools and processes in place for rapid development of an updated Covid-19 vaccine if it should be necessary."