The U.S. drug regulator gave Moderna Inc clearance to speed up output of its COVID-19 vaccine by letting it fill a single vial with up to 15 doses, with the United States banking on rapid immunisation to stem the spread of the deadly virus.

The U.S. Food and Drug Administration (FDA) also authorized vaccinators to extract a maximum of 11 doses from the current vials, instead of the ten previously permitted. In a statement, Moderna said its vaccine can now can be supplied in vials containing 11 or 15 doses, and it expected to begin shipping 15-dose vials in coming weeks.

"Both of these revisions positively impact the supply of Moderna COVID-19 Vaccine, which will help provide more vaccine doses to communities and allow shots to get into arms more quickly," Peter Marks, director of FDA's Center for Biologics Evaluation and Research, said. However, the regulator also warned that without proper syringes and needles it may not be possible to extract more that 13 doses from Moderna's 15 dose vials, and more than 10 doses from the current vials.

Moderna has supplied 100 million doses of its vaccine to the United States as of March 29. Pfizer/BioNTech and Johnson & Johnson's shots are the other two vaccines approved in the country. With rising cases and several states even lifting mask mandates and with more infectious variants also spreading, health authorities are hoping that the contracts it struck with the currently approved vaccine makers will be enough for its entire population.

U.S. top infectious diseases doctor Anthony Fauci told Reuters on Thursday that the country may not need AstraZeneca's COVID-19 vaccine even if it wins U.S. regulatory approval.