WASHINGTON (AP) — The Trump administration will pay Pfizer nearly US$2 billion for a December delivery of 100 million doses of a COVID-19 vaccine the pharmaceutical company is developing, Health and Human Services Secretary Alex Azar announced today.

The US could buy another 500 million doses under the agreement, Azar said.

“Now those would, of course, have to be safe and effective” and approved by the Food and Drug Administration, Azar said during an appearance on Fox News.

Pfizer Inc and BioNTech SE announced separately that the agreement is with HHS and the Defense Department for a vaccine candidate the companies are developing jointly. It is the latest in a series of similar agreements with other vaccine companies.

The agreement is part of President Donald Trump’s Operation Warp Speed vaccine programme, under which multiple COVID-19 vaccines are being developed simultaneously. The programme aims to deliver 300 million doses of a safe and effective COVID-19 vaccine by January 2021.

Under the initiative, the government will speed development and buy vaccines — before they are deemed safe and effective — so that the medication can be in hand and quickly distributed once the FDA approves or authorises its emergency use after clinical trials.

Pfizer and BioNTech said the US will pay US$1.95 billion upon receipt of the first 100 million doses it produces, following FDA authorisation or approval.

Americans will receive the vaccine for free, the companies said.

Azar said the contract brings to five the number of potential coronavirus vaccines that are under development with US funding. Nearly two dozen are in various stages of human testing around the world, with several entering final test to prove if they really work.