Novavax Inc on Thursday again delayed its timeline for seeking US authorization for its 2-dose COVID-19 vaccine but expects to become a major distributor to lower and middle-income countries this year.

It had previously said it would seek emergency use authorization (EUA) from the US Food and Drug Administration in the third quarter of 2021 but now expects to file in the fourth quarter.

Novavax shares dropped around 7 percent in after-hours trading.

"It's a matter of getting validation work done" to demonstrate consistency in the vaccine's manufacturing process to the FDA, said Chief Executive Officer Stanley Erck during an interview with Reuters.

He added that other countries' regulators have been more aggressive in moving Novavax's vaccine through the authorization process.

The company said it has filed for regulatory authorization for its shot in India, Indonesia and the Philippines.

"Initially, our doses may be prioritized to low-income countries, where we'll be able to support critical unmet demand for primary vaccinations," Erck said during Novavax's quarterly investor call.

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Despite promising clinical data, the Maryland-based company has lagged rival vaccine makers such as Pfizer Inc and Johnson & Johnson. It has repeatedly delayed regulatory filings and the timeline for ramping up production as it struggled to access raw materials and equipment needed to produce the vaccine.

Erck said Novavax remained on track to produce 100 million doses per month in the current quarter and 150 million doses by the fourth quarter.

Erck told Reuters the company is on track to submit a regulatory filing in the United Kingdom in September followed within weeks by submissions in Australia and Canada.

Separately, Novavax said a single booster shot of its vaccine given 6 months after an initial 2-dose regimen, elicited a 4.6-fold increase in antibodies.

According to Erck, the company will file a separate application for booster shots with the FDA once its emergency use authorization submission is processed.

"We appear to have got past (certain) supply issues and are now being able to produce at scale," Erck told Reuters.

• Philippines to get 13M Novavax vaccines by third quarter of 2021: official

Novavax has already manufactured tens of millions of shots and is not worried about them expiring before they are approved for use because the vaccine material is kept frozen, Erck said during the investor call.

The drugmaker said it has expanded its late-stage US trial to include pediatric patients and has enrolled more than 2,000 volunteers between 12 and 17 years old. Both rivals Moderna and Pfizer have already initiated trials of their vaccines in children under the age of 12.

In May, FDA authorized the vaccine developed by Pfizer and its German partner BioNTech for use in children ages 12 to 15 years while Moderna's application for use of its vaccine in teenagers is under review.

Novavax reported a net loss of $352 million, or $4.75 per share, for the second quarter of 2021, far higher than its net loss of $18 million for the same period in 2020. Its second-quarter revenue was $298 million.

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