WASHINGTON (AP) — Pfizer and BioNTech will supply the U.S. with an additional 100 million doses of their COVID-19 vaccine under a new agreement. The drugmakers said Wednesday that they expect to deliver all the doses by July 31. The additional doses are on top of 100 million doses Pfizer already was under contract to supply to the government. Two doses are needed for the vaccine to be fully effective. Pfizer’s vaccine was the first to gain emergency authorization from the Food and Drug Administration and initial shipments went to states last week. It has now been joined by a vaccine from Moderna.