The study of nearly 30,000 volunteers in the United States and Mexico puts Novavax on track to file for emergency authorisation in the US and elsewhere in the third quarter of 2021, the company said.

The protein-based vaccine was more than 93 per cent effective against the more easily transmissible predominant coronavirus variants that have caused concern among scientists and public health officials, Novavax said on Monday.

Protein-based vaccines are a conventional approach that use purified pieces of the virus to spur an immune response, such as those used against whooping cough and shingles.

While the trial was being conducted, the virus variant first discovered in the United Kingdom and now known as the Alpha variant was the most common circulating in the United States, the company said.

The concerning variants first identified in Brazil, South Africa and India were also detected among the trial's participants, Novavax's head of research and development Gregory Glenn said.

The vaccine was 91 per cent effective among volunteers at high risk of severe infection and 100 per cent effective in preventing moderate and severe cases of COVID-19.

It was roughly 70 per cent effective against virus variants that Novavax was unable to identify, Glenn said.

"Practically speaking, it's very important that the vaccine can protect against a virus that is wildly swinging around" in terms of new variants, Glenn said.

Novavax said the vaccine was generally well tolerated. Side effects included headache, fatigue and muscle pain and were generally mild. A small number of participants experienced side effects described as severe.

Novavax remains on track to produce 100 million doses per month by the end of the third quarter of 2021 and 150 million doses per month in the fourth quarter of 2021, the company said.

Chief executive Stanley Erck told CNBC it is possible the United States could donate the 110 million shots Novavax has agreed to supply to the US government to the COVAX program that provides COVID-19 vaccines to poorer countries.

The Maryland-based company has repeatedly pushed back production forecasts and has struggled to access raw materials and equipment needed to manufacture its vaccine.

However, in a May investor call, Erck said major manufacturing hurdles have been cleared and that all of its facilities can now produce COVID-19 vaccine at commercial scale.

Erck said Novavax has begun its regulatory filing in India in partnership with the Serum Institute of India (SII), which is contracted to make Novavax shots.

Erck said his understanding is that SII is no longer constrained by raw materials shortages.

SII had said in March that US restrictions on exports of supplies used for vaccines were limiting its ability to scale up production.

Novavax shares were off 3 per cent in midday trading.

Australian Associated Press