Vaccines Have Decreased Efficacy Against Delta Variant, Still Reduce Infection Risk by 2/3, CDC Finds

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A nurse reaches for a vial of Pfizer-BioNTech Covid-19 vaccine at a pop up vaccine clinic in the Arleta neighborhood of Los Angeles, California, August 23, 2021. The US Food and Drug Administration on August 23, fully approved the Pfizer-BioNTech Covid shot, triggering a new wave of vaccine mandates as the Delta variant batters the country. (Photo by ROBYN BECK/AFP via Getty Images)

The Centers for Disease Control published a study on Tuesday that found that while vaccine efficacy against the delta variant of covid-19 is moderately decreased, vaccines still lower infection risk for the SARS-CoV-2 virus by two-thirds. The study reported the efficacy of Pfizer and Moderna's vaccines against the virus dropped from about 90 percent to 66 percent once the delta variant became the dominant strain. This study comes one day after the U.S. Food and Drug Administration announced its full approval of Pfizer’s covid-19 vaccine on Monday. The announcement is expected to improve vaccination rates and push into effect private and public employer vaccine mandates, which had been contingent on FDA’s action. We’ll discuss the study and the effects of the first covid-19 vaccine FDA authorization and take your questions.


Dr. Robert Wachter, professor and chair in the Department of Medicine, University of California, San Francisco