The drugmakers said Wednesday that they expect to deliver all the doses by July 31. Pfizer already has a contract to supply the government with 100 million doses of its vaccine, which requires two doses per patient. Under the nearly $2 billion deal announced Wednesday, the companies will deliver at least 70 million of the additional doses by June 30, with the remaining 30 million doses to be delivered no later than July 31. The government also has the option to acquire up to an additional 400 million doses.