“We are still in the middle of the fight,” said Eli Rosenberg, a State University of New York at Albany epidemiologist who was not part of the study. “We’re all tired, and we’re all hoping for a vaccine. This shows us how it’s not over here, not even by a long shot.”

Researchers at Stanford University and Ascend Clinical laboratory, a company that processes lab tests for kidney dialysis patients, examined leftover blood plasma samples from a randomly selected group of 28,500 patients. Each person underwent dialysis at one of 1,300 centers in 46 states in July. Testing the plasma revealed about 8 percent had coronavirus antibodies, the molecules the immune system churns out to help fight an infection.

That’s equivalent to about 9 percent of all U.S. adults, according to Stanford University biostatistician and study co-author Maria Montez-Rath, who used patient data on region, age and sex to translate that result to the general populace. Ongoing CDC studies of leftover medical samples — not only from dialysis patients — in 10 regions found roughly similar percentages of people who had antibodies in the summer months.