Merck’s factory in West Point, Montgomery County, has been tapped to help expand production of rival Johnson & Johnson’s COVID-19 vaccine, Merck announced Thursday.

A Merck factory in Durham, N.C., will manufacture the key drug component of the vaccine, but workers at the West Point facility will mix it with other ingredients and fill vials with the vaccine, which is different from the others on the market because it requires one dose instead of two and is easier to store.

At the earliest, Merck could begin manufacturing the vaccine and filling vials in West Point, Merck’s largest pharmaceutical plant, in late May, the company said.

“We’re seeing two health companies — competitors — each with over 130 years of experience, coming together to help write a more hopeful chapter in our battle against COVID-19,” President Joe Biden said Wednesday at a White House event with the chief executives of Merck and J&J. He called the work by the companies “a historic, nearly unprecedented collaboration.”

During that event, Biden also announced that the administration was doubling its order of the J&J vaccine to 200 million doses. The Food and Drug Administration approved the vaccine on Feb. 27.

The J&J vaccine has advantages over the Moderna and Pfizer vaccines, which have been available since December, in that it can be stored in refrigerators for months, rather than in the much colder freezers required for the two others. Because it’s a one-dose treatment, more people can be vaccinated more quickly.

The U.S. Department of Health and Human Services said on March 2, when Biden announced the J&J-Merck collaboration, that it would pay Merck $105 million to “upgrade and equip Merck facilities to the standards necessary to safely manufacture the vaccine.”

On Thursday, Merck declined to say whether any of that money would be used in Montgomery County.

“At Merck we’re proud to contribute to the global response to the pandemic,” Merck’s chief executive, Ken Frazier, said Wednesday at the White House.

The West Point factory employs 4,000 people in manufacturing, among a total of about 7,300 there. It is also a major research site for Merck, which is the largest employer in Montgomery County, and headquarters for Merck’s global vaccines business.

The company, based in Kenilworth, N.J., manufactures 11 vaccines in West Point, including RotaTeq and two versions of Gardasil. RotaTeq protects against rotavirus infections, which cause severe diarrhea in young children. RotaTeq had $797 million in revenue last year. Gardasil is used to protect against the human papillomavirus, which causes oral and genital cancers. It accounted for nearly $4 billion in revenue last year.

Merck’s total revenue in 2020 was $48 billion. It employed 74,000 globally, including 27,000 in the United States.

Among the world’s largest vaccine manufacturers, Merck was in the running to develop one for COVID-19 but gave up in January, writing off a $305 million investment, because in early trials its two vaccine candidate were less effective than others that were already available. It is still working on COVID-19 treatments.