The companies manufacturing COVID-19 vaccines told a House panel on Tuesday that they expect to deliver an additional 140 million doses in the next five weeks, vastly increasing the supply to date and making it possible for most Americans to be inoculated by the end of summer.

Executives with Pfizer and Moderna, the two companies so far authorized to provide vaccines in the United States, said they’ve figured out how to surmount production challenges and don’t foresee shortages in raw materials, allowing them to pledge that they will have delivered a total 220 million vaccine doses through the end of March, up from the roughly 80 million doses supplied since mid-December.

“We do believe we’re on track,” Moderna President Stephen Hoge told U.S. Rep. Diana DeGette, D-Denver, and other lawmakers during a remote hearing of the House Energy and Commerce oversight and investigations subcommittee.

DeGette, who chairs the subcommittee, called Hogue and executives from Moderna, Johnson & Johnson, AstraZeneca and Novavax Inc. – the latter three drug makers with vaccines in the pipeline for approval in the U.S. – to explain what they’ve been doing to ramp up production and say whether they will meet commitments made to the federal government.

“It is often said, vaccines don’t save lives – vaccinations do,” DeGette said in opening remarks, noting that celebration has been in short supply as the “grim milestone” of 500,000 deaths from coronavirus approached. “But with this vaccination program underway, there is hope that we can begin to turn the tide against the virus.”

DeGette said the two companies with approved vaccines fell short of the number of doses they had said they could deliver late last year and hadn’t caught up yet.

Pointing to an announcement last week by President Joe Biden that every American who wants a vaccine should be able to get one by the end of July, DeGette said she “look[ed] forward to exploring solutions” with the executives.

Said DeGette: “That is why it is critical for us to hear today a straightforward assessment from each company about where their manufacturing capacity stands, how much vaccine they anticipate being able to produce, and when they believe they will meet those milestones.”

Pfizer and Moderna said they anticipate being able to increase their output to a combined 28 million doses a week, nearly double the recent delivery. By this summer, the two companies’ executives said, they will be able to complete the order placed by former President Donald Trump’s administration for 300 million doses each.

A vaccine produced by Johnson & Johnson – requiring just a single dose, rather than the two doses needed for the Pfizer and Moderna vaccines – is expected to receive emergency-use authorization as soon as this weekend.

Richard Nettles, vice president of medical affairs for Johnson & Johnson’s Janssen Pharmaceutical Companies, said the company can ship about 2 million doses as soon as it gets the OK and provide an additional 18 million doses by the end of March. By sometime this summer, he said, expect delivery of 100 million doses.

As of Tuesday, Colorado had received 1.4 million doses of the Pfizer and Moderna vaccines and 1.2 million have been administered, according to Centers for Disease Control and Prevention data. Roughly 400,000 Coloradans have received both required doses – about 7% of the population age 18 and older – and more than 400,000 have just gotten their first dose.

DeGette cautioned that vaccines are “only part of the solution to ending the pandemic.”

Americans, she added, should continue wearing masks and practicing social distancing even if they’ve been vaccinated, until drug companies have determined that the vaccines don’t just prevent illness but also prevent transmission of the virus.