Covid-19 vaccine manufacturers are ramping up production, churning out far more doses a week than earlier in the year, progress that is accelerating mass vaccination campaigns in the U.S. After a slow start, Pfizer Inc., its partner BioNTech SE and Moderna Inc. have raised output by gaining experience, scaling up production lines and taking other steps like making certain raw materials on their own.

Pfizer figured out how to stretch scarce supplies of special filters needed for the vaccine production process by recycling them. Moderna shortened the time it needed to inspect and package newly manufactured vials of its vaccine. The companies—along with Johnson & Johnson, which recently launched a Covid-19 vaccine—also are teaming up with other firms to further increase production.

In addition, the U.S. government has helped vaccine makers access supplies under the Defense Production Act, suppliers and government officials say. The Biden administration this month said it used the act to provide $105 million in funding to help Merck & Co. make doses of J&J’s Covid-19 vaccine and to expedite materials used in its production.

Moderna is planning to increase the number of doses in each vaccine vial to 15 from 10.

The improvements and addition of J&J’s shot promises to boost supplies in the U.S. as health authorities accelerate efforts to inoculate enough people to lift restrictions and reopen schools, businesses and other establishments. The U.S. monthly output for the three authorized vaccines is expected to reach 132 million doses for March, nearly triple the 48 million in February, according to estimates by analysts at Evercore ISI.

“We really should expect over the course of the next month or so a very substantial increase in supply” in the U.S., said Eric Toner, senior scholar with the Johns Hopkins Center for Health Security. Early bottlenecks sourcing materials “have been fixed.” The global supply of Covid-19 vaccines also is increasing, though access to supplies and the pace of vaccinations vary widely by country. Companies including AstraZeneca PLC and the Serum Institute of India expect to have produced billions of doses of Covid-19 vaccines by the end of this year.

Vaccines are crucial, health experts say, in protecting people against severe cases of Covid-19 and moving past the pandemic and all its restrictions.