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 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.”