Merck & Co Inc will help make rival Johnson & Johnson's single-shot COVID-19 vaccine in a partnership set to be announced on Tuesday by US President Joe Biden, a White House official said on Tuesday.

After scrapping development of its own COVID-19 vaccine candidates in January, Merck last month said it was working on a deal to open up its manufacturing capacity to other vaccine makers.

The deal with J&J comes just days after the US government authorized its one-dose COVID-19 vaccine and as the company looks to increase its production. The drugmaker said on Monday it was working on signing up new manufacturing partners.

J&J is shipping about four million doses of its vaccine in the United States this week, but the next shipments hinge on when its new, larger manufacturing plant receives regulatory approvals.

The drugmaker expects to deliver another 16 million doses by the end of this month.

J&J's vaccine is expected to be easier to distribute because it only needs to be refrigerated, while vaccines from Pfizer Inc /BioNTech SE and Moderna Inc need to be frozen. Those vaccines also require two shots.

The drugmaker will dedicate two US facilities to J&J's vaccine, according to a report in the Washington Post, which first reported the news of the arrangement on Tuesday.

"Merck remains steadfast in our commitment to contribute to the global response to the pandemic," the company said.

J&J did not immediately respond to a Reuters request for comment.