Novavax Inc's chief executive said on Monday its COVID-19 vaccine could be cleared for use in the United States as soon as May if US regulators authorize it based on data from the company's British trial, which could be completed as soon as April.

But he added that talks with the US Food and Drug Administration are ongoing and the FDA may require that Novavax submit data from its US trial, which could take an additional two months to read out and push back US clearance to mid-summer.

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 United States when it receives authorization, Chief Executive Stanley Erck said.

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

• AstraZeneca closed for COVID-19 vaccine orders; gov't helps firms get Novavax jabs
• Moderna might apply for EUA of COVID-19 vaccine in ‘next few weeks,’ Novavax to follow: FDA

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, Erck said.

Novavax shot would be the fourth to receive authorization for use in the US Johnson & Johnson's vaccine was given clearance on Saturday. Pfizer Inc and Moderna Inc were authorized in December.

Novavax's shot is a two-dose regiment like Pfizer's and Moderna's but is easier to ship as it can be stored at refrigerator temperatures, rather than in a freezer.

Novavax on Monday reported that its net loss widened to $177.6 million, or $2.70 per share, in the fourth quarter, from $31.8 million, or $1.13 per share a year earlier.

Boosted by vaccine business, revenue rose to $279.7 million from $8.8 million a year earlier.

Novavax shares rose as much as 2.4% after it announced earnings Monday.

Novavax promised to deliver doses to the United States after it was awarded $1.6 billion to help finance research, development and production of a COVID-19 vaccine.

An early data readout in January from its UK trial showed the vaccine to be around 96% effective against the original version of the coronavirus and around 86% effective against the now widely circulating variant first discovered in Britain.

Novavax completed enrollment of its 30,000-subject US-based trial in February.