Doses of the Johnson & Johnson COVID vaccine is packaged in a box at the McKesson facility on March 1, 2021 in Shepherdsville, Kentucky.Timothy D. Easley | Getty ImagesPresident Joe Biden will announce Tuesday that pharmaceutical giant Merck will help make Johnson & Johnson’s Covid-19 vaccine, a senior administration official confirmed to NBC News.The announcement comes as the administration works to ramp up the 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. Sixteen 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, according to NBC News. One facility will make the vaccine itself while the other will provide “fill-finish” services, the last stage of the production process during which the vaccine is placed in vials.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, according to NBC News. They soon sought a deal with Merck, which scrapped plans to develop its own Covid-19 vaccine in January after a clinical trial showed its shots were ineffective.J&J declined to comment to CNBC on the deal. 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.”The FDA 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 ultra-cold 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.This is a developing story. Please check back for updates.