The U.S. government’s description of a final coronavirus vaccine it plans to add to its multi-billion dollar “Operation Warp Speed” program closely matches the details of experimental inoculations being developed by Merck & Co.

During a presentation Wednesday, Moncef Slaoui, Warp Speed’s chief adviser, described a “TBD,” or to-be-determined, vaccine that has not yet been announced. It would be a “live attenuated” vaccine -- which uses weakened viruses that replicate in the body but don’t cause disease, and would be administered in a single dose, potentially in oral form rather than an injection, Slaoui said.

Merck has two coronavirus vaccines in development that match that description, relying on the same technology and being tested as a single dose. One of the two vaccines is being evaluated in oral form. Bloomberg reported in June that Merck was involved in the Warp Speed program, though no formal agreement with the company has been publicly announced.

Merck shares reversed earlier losses and were up less than 1 per cent to US$82.67 at 10:08 a.m. in New York

A representative for Merck declined to comment. The Department of Health and Human Services, which is helping oversee the Warp Speed program, also declined to comment.

The U.S. is supporting multiple experimental vaccines, awarding grants to companies worth a billion dollars or more to fund clinical development and the manufacturing of millions of doses while final trials are still underway. The program is meant to cut years off of typical vaccine development timelines, potentially saving tens of thousands of lives and helping to restore life in the U.S. back to normal.

Merck Chief Executive Officer Kenneth Frazier told Bloomberg in May, when the company announced two vaccine candidates, that his goal was to deliver a vaccine that was effective in a single dose, making it easier to use. Vaccines under development by front-runners Moderna Inc., Pfizer Inc. and AstraZeneca Plc., require a first shot and then a booster several weeks later. On Wednesday, Johnson & Johnson announced that it had started its own final-stage tests of its vaccine, which will test a single dose in the U.S.

Merck researchers are attempting to make an oral formulation of the Covid-19 vaccine based on their Ebola vaccine, letting patients take it by swishing a solution around their mouths and swallow. Merck’s top scientist and R&D leader Roger Perlmutter said on a July 31 call with investors that an orally-available option “will help to lower the barrier to vaccination.”

So far, large Warp Speed deals have been announced for a total of six vaccines under development by Moderna, Pfizer and BioNTech SE, Johnson & Johnson, AstraZeneca, Novavax Inc., and Sanofi and GlaxoSmithKline Plc.

In August, Slaoui and Matthew Hepburn, a Department of Defense official, wrote in the New England Journal of Medicine that the U.S. has aimed to secure eight vaccine candidates that span four different types of technologies: messenger RNA, non-replicating live vectors, recombinant-subunit adjuvanted protein and attenuated replicating live-vector vaccines.

While the U.S. has announced deals for vaccines in the first three categories, it has not announced any in the final type, which is based on an older, more proven technology.

Slaoui and Hepburn said in the journal article that the “remaining two candidates will enter trials soon.” One of Merck’s vaccines started tests this month, and the other is set to begin before the year’s end.

“At this stage we have not yet publicly announced what program we are selecting,” said Slaoui during a meeting of the National Vaccine Advisory Committee, which advises the U.S. Department of Health and Human Services.

Merck’s agreement with the U.S. government’s Biomedical Advanced Research and Development Authority was made in April for US$38 million, and was for early development work on one of the vaccines. Many of the Warp Speed deals are much larger, with some as large as US$2 billion.