COVID-19 vaccine makers told Congress on Tuesday to expect a big jump in the delivery of doses over the coming month after a rocky start to inoculations, and the companies insist they will be able to provide enough for most Americans by summer.

By the end of March, Pfizer and Moderna expect to have provided the U.S. government with a total of 220 million vaccine doses, up from the roughly 75 million shipped so far.

“We do believe we’re on track,” Moderna President Stephen Hoge said, outlining ways the company has ramped up production. “We think we’re at a very good spot.”