WASHINGTON • Novavax's coronavirus vaccine could be cleared for use in the United States as soon as May if US regulators authorise it based on data from the company's British trial, which could be completed "in the coming weeks", its chief executive said on Monday.

However, chief executive Stanley Erck added that talks with the US Food and Drug Administration are ongoing and the agency may require Novavax to submit data from its US trial, which could take an additional two months to complete, pushing back US clearance to mid-summer.

Novavax shares were off 5.6 per cent at US$226.85 in extended trading after initially rising following the release of its quarterly results. The shares have soared about 2,400 per cent from US$9.82 on Jan 21 last year, when the company announced it was developing a vaccine against the coronavirus.

Preliminary data from its British trial released in January showed the vaccine to be about 96 per cent effective against the original version of the coronavirus and around 86 per cent effective against the now widely circulating variant first discovered in Britain.

Novavax can already manufacture its shots at scale and will be able to have tens of millions of doses stockpiled and ready to ship in the US when it receives authorisation, Mr Erck said.

"It will be substantial - in the many tens of millions or a hundred million," he said in an interview.

Novavax had promised to deliver 110 million doses to the US government by the end of the third quarter. That could happen as early as July, he added.

Novavax's vaccine production plants should all be fully functional by next month, said Novavax research chief Gregory Glenn in a conference call after the company reported quarterly results.

"In April, May, June, we should be finishing filling and finishing product in advance of regulatory approvals," he added.

In late January, Mr Erck said he expected it would take several weeks for Novavax to file British trial data with regulators in Britain, Europe and elsewhere. Novavax could produce up to 150 million doses per month by May or June, he had added in January in an interview.

The Novavax shot, if authorised, would add to the vaccine options for millions of Americans awaiting immunisation against the coronavirus.

Johnson & Johnson's one-dose vaccine last Saturday became the third to win US emergency use authorisation.

Vaccines produced by Pfizer with partner BioNTech and Moderna received emergency use authorisation in December.

Novavax's vaccine is a two-dose regimen like Pfizer's and Moderna's, but is easier to ship as it can be stored at refrigerator temperatures instead of having to be frozen.

Novavax promised to deliver doses to the US after the Trump administration awarded it US$1.6 billion (S$2.1 billion) to finance research, development and production of a Covid-19 vaccine.

It also completed enrolment of its 30,000-subject, US-based trial last month.

REUTERS