Merck & Co 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. J&J's vaccine production has been slower than promised.
Under its contract, the company was supposed to deliver 12 million doses by the end of February, but had fewer than four million ready to ship when the vaccine was authorised on Saturday.
It expects to be able to deliver another 16 million doses by the end of the month - still well short of its previous commitments - but will not ship any next week. The company has said it will be able to provide the full 100 million doses it has agreed to supply by its original mid-year deadline.
The next shipments are awaiting regulatory approval of new manufacturing operations run by its partner, contract drug-maker Catalent, J&J chief scientific officer Paul Stoffels said in an interview on Monday.
Stoffels also said the company was looking for more partners to expand its production capacity. More doses sooner could speed the US vaccination effort considerably, because as a one-dose vaccine it is possible to inoculate twice as many people with the same number of shots.
The other two US-approved vaccine, from Pfizer and BioNTech, and Moderna, require two doses. J&J's vaccine substance is made in the United States at a plant operated by Emergent BioSolutions, as well as at facilities in the Netherlands and India.
Merck's collaboration with J&J comes after Merck scrapped 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.