The United States on Tuesday announced it was providing $1.6 billion in funding for the development and manufacture of a COVID-19 vaccine candidate produced by biotech firm Novavax, the largest amount awarded under Operation Warp Speed.

Separately, the US also said it was providing $450 million to Regeneron for its experimental COVID-19 treatment and prophylaxis, a combination of two antibodies.

Under the terms of its agreement with the Department of Health and Human Services (HHS) and Department of Defense, Novavax agrees to deliver 100 million doses of its vaccine, potentially by the end of the year.

"We are honored to partner with Operation Warp Speed to move our vaccine candidate forward with extraordinary urgency in the quest to provide vital protection to our nation's population," said Stanley Erck, the company's president and CEO.

The final stage Phase 3 trial of its vaccine, called NVX-CoV2373, is set to take place this fall.

The Maryland-based company uses insect cells to grow synthesized pieces of the SARS-CoV-2's "spike protein," which the virus uses to invade cells, in order to trigger the human body's immune response.

It also uses an "adjuvant," a compound that boosts the production of neutralizing antibodies.

In the spring, the company said it had proven the efficacy of a seasonal flu vaccine it had developed using similar technology.

The amount awarded to Novavax by the US is higher than the $1.2 billion given to the Oxford University vaccine that is being developed by AstraZeneca.

Under Operation Warp Speed, the US is aiming to deliver millions of doses of safe and effective vaccines for COVID-19 in 2021.

Also Tuesday, the US said it was providing New York-state based Regeneron with $450 million to scale up manufacture of its COVID0-19 antibody treatment.

The company, which announced on Monday it was entering late stage human trials, estimates that it could have between 70,000 and 300,000 treatment doses, with the first available by late summer.

The drug, called REGN-COV2, is a combination of two antibodies that block the coronavirus' spike protein.

Regeneron scientists evaluated thousands of antibodies harvested from genetically-modified mice with human immune systems and from humans, identifying the two they found to be most potent, while not competing against each other.

The company uses a multi-antibody strategy to decrease the chances that the virus will mutate in order to evade the blocking action of a single antibody, an approach it detailed in a recent study in Science.

Last year, a triple antibody cocktail developed by Regeneron was shown to be effective against the Ebola virus.