“Today’s submission of our protein-based COVID-19 vaccine to WHO for emergency use listing is a significant step on the path to accelerating access and more equitable distribution to countries in great need around the world,” Stanley Erck, president and CEO of Novavax, said in a press release on Thursday.

Novavax’s jab would be the first protein subunit COVID-19 vaccine to win WHO approval, and the technology, which trains the immune system to fight COVID-19 through a protein that contains part of the disease pathogen, offers several distinct advantages over other vaccines.

Unlike mRNA shots from Pfizer and Moderna that require sub-zero temperatures for transport and storage, Novavax’s shots can be kept at normal refrigerated temperatures (2 to 8 degrees Celsius).

In trials, Novavax’s vaccine produced less severe side effects than the mRNA jabs even as it demonstrated similar efficacy against the virus. Phase III trials showed that the vaccine was 90.4% effective in preventing symptomatic cases of COVID-19. Novavax also said in early August that a booster dose of its vaccine created six times more antibodies associated with fighting off the Delta variant of COVID-19 than its initial two-dose regimen.

But the challenges facing Novavax do not stem from how well the vaccine appears to work. Rather, Novavax has struggled to find a way to produce its shots. (Novavax did not respond to Fortune’s request to comment.)

Novavax says it is currently producing COVID-19 vaccines at 20 plants globally and will have the capacity to make 2 billion vaccines in 2022, but none of the firm’s vaccines are currently being used beyond clinical trials.

In the U.S., Novavax has yet to apply to the Food and Drug Administration (FDA) for emergency use authorization and says it may not apply for approval until the fourth quarter of this year after months of delays. 

U.S. regulators told the New York Times in August that the hold-up stemmed from poor quality control at Novavax’s manufacturing facilities. Novavax later said a contract it signed with the U.S. government has constrained its ability to produce doses. Since July 2020, Novavax has received $1.75 billion from former President Donald Trump’s Operation Warp Speed to develop and manufacture its vaccines. As part of the deal, Novavax says that it was directed to work with manufacturers including the Japanese-owned and U.S.-headquartered pharmaceutical manufacturer Fujifilm Diosynth Biotechnologies, which has slowed production.

“We don’t have control over all the timelines with the outside firms we have to use,” Novavax CEO Erck told Yahoo in August, saying Fujifilm’s Texas plant had “quality issues.” Fujifilm and Novavax later issued a joint statement that said Novavax’s delays were related to a need for further “analytical work” that Fujifilm is not responsible for.  

Outside of the U.S., Novavax signed a deal with the Serum Institute of India in August 2020 that provided SII with the rights to manufacture and distribute its vaccine under the name Covavax in India.

This spring, Novavax and SII pledged to send 1.1 billion doses of the Novavax vaccines to COVAX, the global facility to share vaccines among lower- and middle-income countries, and planned to start vaccine shipments in the third quarter of 2021 to countries around the world.

But the Serum Institute of India, the world’s largest vaccine manufacturer by volume, says that regulatory delays in the U.S. has hampered the SII’s ability to manufacture and distribute vaccines.

“We will get the license only when the company gets one from the (U.S.) FDA. We are trying to obtain the license ahead of the parent company, but it’s an uphill task,” Cyrus Poonawalla, chairperson of SII, told Indian media in August.

Adar Poonawalla, Cyrus’s son and CEO of SII, said last week that Novavax has struggled to obtain raw materials, but expects supply constraints to ease in coming months.

“Developing new supplies takes time,” the younger Poonawalla told India’s Business Standard. “The silver lining is we have got people who can make quality raw materials, but they are inundated with orders from different vaccine companies—from Korea, China, Europe, etc.”

India’s top health minister Mansukh Mandaviya said Monday that India would resume COVID-19 vaccine exports next month, potentially clearing one additional hurdle for SII and Novavax to ship doses to COVAX if the WHO approves the jab and Novavax can start manufacturing doses.

“We will help the world and also fulfill our commitment toward COVAX,” Mandaviya said.

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