What are clinical trials and how do they work?
Data from such trials have shown that two vaccines -- one developed by Pfizer and BioNtech, the other by Moderna and the US National Institutes of Health -- are about 95 percent effective.Data from such trials have shown that two vaccines -- one developed by Pfizer and BioNtech, the other by Moderna and the US National Institutes of Health -- are about 95 percent effective.
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