The U.S. government placed an order with Pfizer for what could amount to 600 million doses of a potential COVID-19 vaccine.

The federal government placed an initial order of 100 million doses for $1.95 billion. It can then acquire up to 500 million more doses.

Pfizer said Americans would receive the vaccine for free.

The drug maker, which partnered with the German company BioNTech for the vaccine, said it remains on track to begin an anticipated “Phase 2b/3” safety and efficacy trial later this month. It could seek regulatory review as early as October 2020.

The global manufacturing of up to 100 million doses could happen by the end of 2020 with potentially more than 1.3 billion doses by the end of 2021.