“Because of the dire need to vaccinate more people, we have ramped up production of doses,” John Young, Pfizer’s chief business officer, told the House Energy and Commerce oversight and investigations subcommittee in prepared testimony.

But achieving a surge on that scale remains daunting. Pfizer and Moderna, the companies with the only authorized vaccines so far, will need to increase their combined deliveries to date of 75 million doses to reach their promised target of 220 million shots by March 31.

That’s a goal of 28 million doses each week on average, far greater than their performance so far. The Biden administration said last week that doses allotted to states would grow from 11 million to 13.5 million per week, and it also directed 2 million doses to pharmacies, part of allocations that are expected to increase modestly again this week.

If the companies are able to meet their projections, it would signal the beginning of the end of a period of deep frustration and mark faster progress against a pandemic that has claimed 500,000 lives in the United States.