• President Joe Biden announced Tuesday that pharmaceutical giant Merck will help make Johnson & Johnson's Covid-19 vaccine.
• The decision comes as the administration works to ramp up production of J&J's single-shot vaccine.
• Senior administration officials said Sunday the U.S. government would ship J&J's entire inventory of 3.9 million doses this week, adding that supply would be "uneven" in the following weeks.

President Joe Biden announced Tuesday that pharmaceutical giant Merck will help make Johnson & Johnson's Covid-19 vaccine.

The decision comes as the administration works to ramp up production of J&J's single-shot vaccine. Senior administration officials said Sunday the U.S. government would ship J&J's entire inventory of 3.9 million doses this week, adding that supply would be "uneven" in the following weeks. Some 16 million more doses are expected by the end of the month.

Under the arrangement, Merck will dedicate two facilities in the U.S. to J&J's vaccine, the Washington Post reported earlier. One will make the vaccine and the other will provide "fill-finish" services, when the vaccine is placed in vials.

The Department of Health and Human Services said later Tuesday that the U.S. will use Defense Production Act to provide an investment of $105 million for Merck to convert, upgrade and equip the company's facilities to the standards necessary to safely manufacture the vaccine.

Officials began scouring the country for additional manufacturing capacity after they realized in the first days of the administration that J&J had fallen behind in vaccine production, the Post reported. They soon sought a deal with Merck, which scrapped plans to develop its own Covid vaccine in January after a clinical trial showed its shots were ineffective.

"These efforts will contribute to J&J's ability to accelerate delivery of their vaccine doses from 100 million doses by the end of June to at or near 100 million doses by the end of May, " HHS said in a statement. "In the long term, these actions will ultimately double J&J's U.S. capacity to produce drug substance and increase the U.S. capacity for fill-finish."

Later Tuesday, J&J said in a statement that the collaboration with Merck "will enhance our production capacity so that we can supply beyond our current commitments."

In a statement, Merck said it "remains steadfast in our commitment to contribute to the global response to the pandemic and to preparing to address future pandemics."

In an interview with CNBC's Meg Tirrell, Merck's Chief Marketing Officer Michael Nally said the partnership is "very meaningful" and will "add dramatically" to the capacity of the J&J vaccine over time. He declined to provide exact numbers on how Merck's involvement will impact J&J's supply.

He also said the collaboration would not impact the production of Merck's other drugs, adding "this was all capacity that was being oriented for our Covid products."

"We feel really confident that we can continue to produce all our .. vaccines without any sort of interruption," he said. He added the company is open to working with companies and public health agencies on similar collobrations.

The Food and Drug Administration on Saturday authorized J&J's vaccine for use in people 18 and older. Unlike Pfizer's and Moderna's vaccines, J&J's one-dose regimen eliminates the need for patients to return for a second dose, and it can be stored at refrigerator temperatures for months.

By comparison, Pfizer's vaccine needs to be stored in ultracold freezers that keep it between minus 112 and minus 76 degrees Fahrenheit, though the FDA recently allowed the company to store its vaccine for two weeks at temperatures commonly found in pharmaceutical freezers. Moderna's vaccine needs to be shipped at 13 below to 5 degrees above zero Fahrenheit.

The New York Times first reported in January that unexpected manufacturing delays would lead to a reduced initial supply of J&J's drug if it were given emergency authorization.

White House Chief Medical Advisor Dr. Anthony Fauci said last month he was "disappointed" with the number of doses initially expected from J&J, adding the federal government thought there would be "considerably more." The New Jersey-based company has a deal with the U.S. to provide 100 million doses by the end of June.

"It may take until June, July and August to finally get everybody vaccinated," Fauci told CNN on Feb. 16. "So when you hear about how long it's going to take to get the overwhelming proportion of the population vaccinated, I don't think anybody disagrees that that's going to be well to the end of the summer and we get into the early fall."

At the time, Biden's Covid czar, Jeff Zients, said the federal government was doing "everything we can working with the company to accelerate the delivery schedule."

This isn't the first partnership between two drugmakers to help ramp up the vaccine supply.

In late January, French drugmaker Sanofi announced it would help fill and pack millions of doses of Pfizer's two-shot vaccine in an effort to help meet demand. Moderna has a partnership with Swiss company Lonza, which produces most of the drug substances for the company's vaccine.

The Biden administration has also said it is using the Defense Production Act to help ramp up supply of Pfizer's vaccine.