U.S. Pledges $1.2 Billion For Experimental Vaccine Doses

The US has committed $1.2 billion to AstraZeneca for 300 million vaccine doses, with clinical trials starting in April. The doses will be stored until proven effective. AstraZeneca is confident in the vaccine's potential, expecting all doses by December or January. Operation Warp Speed aims for a widely available vaccine by 2021, with phase three trials involving 300,000 US volunteers.

What is the goal of the US Department of Health and Human Services regarding the vaccine by 2021?

How many volunteers are expected to be included in the phase three clinical studies?