Months of talks between Johnson & Johnson (J&J) and Merck & Co. Inc. about a COVID-19 vaccine manufacturing partnership came to fruition March 2 with the Biden administration hailing the deal as an “unprecedented historic” agreement between two long-time rivals.

Speaking at a media briefing, White House Press Secretary Jen Psaki attributed the partnership to an “across-the-administration” effort to bring the rivals together. However, she had to backtrack when a reporter cited a Jan. 21 news report that showed the two companies had been in talks before Joe Biden became president.

Saying she was focusing on what got the partnership across the finish line, Psaki credited Biden with closing the deal by invoking the Defense Production Act to help equip two Merck plants to meet the standards needed to manufacture the drug substance required for the one-dose vaccine and to perform fill/finish processes.

The administration also is asking the U.S. Department of Defense to provide daily logistics support to strengthen the manufacture of the J&J vaccine, which received emergency use authorization Feb. 27, the day following an FDA advisory committee meeting.

Even without the extra manufacturing capacity of the two Merck sites, Psaki said J&J is expected to deliver 2.8 million doses of the vaccine this week and the company is on track to keep its commitment to deliver 100 million doses to the U.S. by the end of June.

Adding Merck’s capacity, which likely will take a few months to scale up, will help J&J reach its global goal of producing 1 billion doses of the vaccine by year-end.

Testifying before a House subcommittee last week, Richard Nettles, vice president of U.S. medical affairs at J&J’s Janssen Infectious Diseases and Vaccines unit, said that since the pandemic took hold last year, J&J has focused on building a global supply network, through collaboration with the government and other companies, in parallel with the development of the vaccine itself.

As part of that effort, the Brunswick, N.J.-based company assessed nearly 100 manufacturing sites to find ones that could handle the complex manufacturing processes required for the vaccine. Nettles told the lawmakers that J&J had selected eight sites that could meet the accelerated production timeline and planned to have seven manufacturing sites active by midyear. At the time of the hearing, J&J already had entered manufacturing agreements with several established companies, including Sanofi SA, another seasoned vaccine developer.

Adding a manufacturing site is not a flip-the-switch endeavor. And once a site is up and running, it takes about two months to produce the drug substance for J&J’s vaccine, due to the time needed to grow the biological cells and then purify the active vaccine, according to Nettles’ written testimony. It then takes another five to six weeks to produce, test and release the finished vaccine.

With various vaccines of its own, Merck has plenty of experience in manufacturing them. The Kenilworth, N.J., company initially jumped into the COVID-19 vaccine race itself with two recombinant viral vector candidates: V-591, which was acquired through the buyout of Vienna-based Themis Bioscience GmbH, and V-590, part of a collaboration with the International AIDS Vaccine Initiative. After phase I data failed to show efficacy, Merck terminated its development of the vaccines.