evidence: Until now, evaluations of vaccine effectiveness amid delta largely relied on observations from outside the United States. A recent New England Journal of Medicine study concluded the Pfizer vaccine was 88 percent effective against infections that caused symptoms in England. Others, such as a study in Israel, found larger declines in protection against infection. One U.S. report that has not yet gone through peer review, collecting data from Mayo Clinic Health System facilities in five states, found a drop in the Pfizer-BioNTech vaccine’s effectiveness against delta infections to 42 percent. The other mRNA vaccine, made by Moderna, was 76 percent effective. The new study from New York is the first to assess vaccine protection against coronavirus infection across the entirety of a U.S. state amid delta. The study authors found a modest drop in effectiveness: It descended from 92 percent in May to 80 percent in late July.