(Reuters) -Novavax ( NVAX ) on Thursday tried to calm investors spooked by the delay of full approval of its COVID vaccine shot by U.S. regulators saying that it sees a pathway to resolving issues with the FDA, sending shares up nearly 19% in early trading.

The vaccine maker said it believes commitments to run new trials would be after it receives approval for the shot.

"Based on what we've received to date, formally from FDA, they're asking for a post-marketing commitment. And by definition, it's our understanding that a post-marketing commitment comes after approval and you've begun to market that product," CEO John Jacobs said in a post-earnings conference call with analysts.

The vaccine's prospects were thrown into doubt after the U.S. Food and Drug Administration missed its April 1 target to approve the shot. U.S. Health and Human Services secretary Robert F. Kennedy Jr. attributed the delay to the shot's composition in a CBS interview earlier that month.

The company said talks with the agency on the proposed study design are ongoing.

"We haven't commented publicly on the nature of the post-marketing commitment at this time, but we continue to work with the FDA diligently and urgently to try to bring this forward as soon as possible to a positive conclusion, and we do see a pathway forward to approval based on the formal comments and questions we've received from FDA," said Jacobs.

The company wants to convert the vaccine's emergency authorization granted in 2022 into a full approval that would allow for expanded use and help it compete against shots from rivals.

Novavax ( NVAX ), whose protein-based shot uses an older technology, missed out on the pandemic vaccine windfall - enjoyed by rivals Moderna and Pfizer which make messenger RNA-based vaccines - due to manufacturing issues and regulatory hurdles.

Novavax ( NVAX ) swung to profit in the first quarter, helped by reduced costs tied to the development and sale of its COVID-19 vaccine, its only product on the market.

  The Maryland-based biotech has been banking on revenue from its Sanofi deal and vaccines in development. It signed a licensing deal worth at least $1.2 billion with the French drugmaker last year to hand over the rights to sell its vaccines in several markets, including the United States and Europe.

Novavax's ( NVAX ) quarterly revenue rose to $667 million in the reported quarter, from $94 million a year ago, and comfortably surpassed analysts' estimate of $343.85 million, according to data compiled by LSEG.

The sales boost was mainly driven by revenue recognition of $603 million following the termination of two advance purchase agreements in Canada and New Zealand and related to cash received in prior years.

The company sees adjusted total revenue for 2025 to be between $975 million and $1.03 billion, more than double its prior expectations of between $300 million and $350 million. This excludes Sanofi sales and royalties.

Net income came in at $519 million for the quarter ended March 31, compared to a net loss of $148 million a year earlier.