Novavax Inc is doubling its Covid-19 vaccine manufacturing capacity to two billion doses under an agreement with Serum Institute of India, the U.S. company said on Tuesday.

In August, Novavax signed a deal with Serum Institute, the world’s largest producer of vaccines, to produce a minimum of one billion doses of its vaccine candidate for low-and middle-income countries and India.

As part of the expanded agreement, Serum Institute will also manufacture the antigen component of the vaccine, which is dubbed NVX-CoV2373.

The U.S. company’s vaccine is in mid-stage trials after an early-stage trial showed it produced high levels of antibodies against the novel coronavirus.

Other drugmakers such as Pfizer Inc and Moderna Inc have already begun large late-stage studies of their experimental vaccines.