evidence: Mayo Clinic researchers are reporting a "pronounced reduction" this summer in the effectiveness of the Pfizer COVID-19 vaccine at preventing coronavirus infections, but still a high level of protection against severe illnesses and hospitalizations. [...] Examining records for 25,000 vaccinated and unvaccinated Mayo patients in Minnesota, the researchers reported 76% effectiveness in the Pfizer vaccine protecting them from infection this year, but only 42% effectiveness in July amid the emergence of a more transmissible delta variant. The comparable effectiveness of the Moderna vaccine declined from 86% to 76%. [...] The effectiveness of the Pfizer and Moderna vaccines at preventing hospitalizations was 85% and 91%, respectively, during the entire year, so their performance in July alone was slightly worse.