Results of a nationwide COVID-19 antibody study indicate herd immunity “remains out of reach” in the U.S., with less than 10 percent of participants testing positive for proteins that could potentially offer protection from repeat infections. The study — conducted by Stanford University researchers in July and published by peer-reviewed medical journal The Lancet on Friday — evaluated the presence of COVID-19 antibodies in blood samples from 28,500 dialysis patients across 46 states. It is one of the largest studies of its kind conducted to date in the U.S.