A COVID-19 Vaccine May Be Only 50% Effective. Is That Good Enough?

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Jesse Zhang for NPR

As we get closer to a COVID-19 vaccine, it’s exciting to imagine a day when the virus is gone. But a vaccine will not be a magic bullet. In fact, it may be only about 50% effective. Dr. Anthony Fauci, chief of the National Institute of Health and Infectious Disease, has tried to set realistic expectations when discussing the importance of a vaccine. “We don’t know yet what the efficacy might be. We don’t know if it will be 50% or 60%,” Fauci said during a Brown University event in August. I’d like it to be 75% or more,” Fauci said, but he acknowledged that may not be realistic. Meanwhile, the Food and Drug Administration has said that once a vaccine is shown to be safe and at least 50% effective it could be approved for use in the U.S. So what does 50% efficacy mean?

“When we talk ‘vaccine effectiveness,’ what we’re talking about is, ‘How effective was the vaccine at preventing actual disease,’ ” explains scientist L.J. Tan, chief strategist of the nonprofit Immunization Action Coalition. In other words, Tan says, “If you vaccinate 100 people, 50 people will not get disease.” This may not sound …

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