As the U.S. continues to battle the COVID-19 pandemic, experts say we may have a fourth vaccine in our arsenal to win the war. AstraZeneca says it plans to seek emergency use authorization for its two-dose shot pending the results of a current U.S. clinical trial.

According to Mediaite, the pharmaceutical giant says if the approval goes smoothly, it is prepared to supply the U.S. with 50 million doses of its vaccine.

There are currently three vaccines that have been awarded emergency use authorization by the government agency. The mRNA two-dose shots from Moderna and Pfizer-BioNTech and the one-dose vaccine from Johnson & Johnson are now available. Government sources say we should have enough vaccines to immunize the entire U.S. population by the end of May.

AstraZeneca says it plans to seek emergency use authorization from the FDA within the next few weeks, according to CBS News. The company’s vaccine is now being shipped to 142 countries worldwide and it says it could supply the U.S. with millions of doses once the vaccine is approved.

''We are prepared to supply tens of millions of doses after the emergency use authorization,'' said AstraZeneca executive vice president Ruud Dobber, adding that his company expects to see the results of its U.S. clinical trial within weeks, after which it will apply for FDA approval.

The AstraZeneca vaccine already has been given the green light by the European Union, the U.K., and the World Health Organization, according to CBS News.

The vaccine that was developed in collaboration with Oxford University in England is made from a weakened version of a common cold virus known as the adenovirus from chimpanzees, according to BBC News. It was modified to resemble the coronavirus but does not cause illness.

Clinical trials found that the efficacy rate of the AstraZeneca vaccine was 62%, but a more recent study found that a single dose offered 76% protection for three months, and this went up to 82% after the second dose, according to BBC News.

Dobber said that AstraZeneca is ''very hopeful" that the vaccine is "effective against the U.K. variant,'' but added that their scientists are in the midst of developing ''a potential new vaccine in case our current vaccine is not as effective as we were hoping for.''