Stock markets around the world have fallen after the boss of Moderna cast doubts on the effectiveness of vaccines against the new Omicron Covid variant.
Stephane Bancel told the Financial Times he thought there would be a “material drop” in vaccine efficacy.
The Covid variant was first detected in South Africa, and the symptoms have been mild so far.
But travel restrictions have been imposed as a precaution by places including the UK, the EU and the US.
Mr Bancel predicted that existing vaccines would be less effective in staving off Omicron, and that it would take months for drugs companies to update vaccines.
“There is no world, I think, where [the effectiveness] is the same level,” he said.
In the US, the Dow Jones Industrial Average was 0.8% lower shortly after trading began. The broader S&P 500 share index dropped 0.6% while the tech-focused Nasdaq was down 0.3%.
That followed steeper falls in Europe and Asia.