NPR News: How Can You Tell If A COVID-19 Vaccine Is Working?

How Can You Tell If A COVID-19 Vaccine Is Working?
Several COVID-19 vaccine candidates are being tested now. But why does it take 30,000 volunteers to know if one is safe and effective? And what does it mean to say a vaccine candidate is working?

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at September 7, 2020 at 04:05PM
Health & Science