Pfizer just recently delivered more than 40 million doses to the U.S.
That's behind its initial schedule, but the company says it still believes it can reach 300 million total doses by July.
"We did initially experience some problems with the ramp up of our vaccine and i think in common with other panelists here we have been in the process of developing a manufacturing process for a vaccine product we have never made before," says John Young who is the group president and chief business officer of Pfizer. "We particularly saw some problems with raw materials but we anticipate we will be on track to deliver those 300 million doses before the end of July."
Pfizer and Moderna are the only companies with FDA approved vaccines.
Johnson & Johnson says it will be ready to ship 20 million doses of its single-shot vaccine once it gets approval.