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Researchers from Stanford University estimated that fewer than one tenth of the American adult population have COVID-19 antibodies, suggesting that the U.S. is still far from achieving herd immunity.

The study relied on blood samples from more than 28,000 randomly selected dialysis patients across the United States who had blood drawn in July. According to the sample, only 8 percent of patients tested had formed COVID-19 antibodies, a figure that translates to 9.3 percent when standardized to the U.S. adult population.

“Most modeling estimates say that we need to get to about 60 or 70 percent of antibody levels in the population,” said Shuchi Anand, the study’s lead author and assistant professor of medicine at the Stanford University Medical Center. “Based on natural infection alone, we’re not there.”

William Hanage, an associate professor of epidemiology at the Harvard School of Public Health, said in a Sept. 25 USA Today article that the study confirms the outbreak in the spring was “ridiculously” underestimated.

“We expect small-town America not to be in the first surge," Hanage, who was not an author on the study, told USA Today.

Normally, researchers would have carried out “community surveys,” knocking on doors and asking if residents would partake in the study. Instead, they obtained free leftover blood plasma from dialysis patients from their industry partner, a commercial laboratory.

The researchers said they believe dialysis patients provide necessary representation for elderly people in addition to racial and ethnic minorities — populations that have experienced disproportionately high rates of COVID-19 infection. Non-Hispanic Black patients had the highest antibody rates at 9.5 percent, 6 percent higher than non-Hispanic white patients; Hispanic patients saw a rate of 6.3 percent.

“We reach a lot of minorities because they are part of our population,” co-author Maria E. Montez Rath said. “And that’s exactly the population that we would want to target more because we know they have had higher rates of COVID.”

In addition to their overall estimate, the researchers noticed a difference in minority groups' antibody rates. The rate of antibody prevalence was lower in older populations than in younger people, the researchers found, while ethnic minority group members were two to four times more likely to have COVID antibodies. The dialysis patient demographic is different to that of the U.S. population, with a greater proportion of older people and ethnic minorities.

Eli S. Rosenberg, an associate professor at University at Albany, estimated the COVID antibody rates in New York in April and weighed in on the difficulties of using residual serum as opposed to traditional sampling methods and the results.

“What's really cool about it is it’s almost every state,” Rosenberg said. “You have more challenges in terms of assuring the representativeness of the sample.”

He added that though the group’s number was probably a “high-end estimate,” their figures still fell “well below” herd immunity.

The group is already trying to answer more questions about COVID-19 by continuing to track their sample group. Dialysis patients must undergo blood draws at least once a month, allowing the researchers to make estimates on how long antibodies remain in the body and how many new COVID cases they have per month.

“Being far away from herd immunity really means that we do need to think at the population level, we do need to think about what can be done, so that we can really protect the vulnerable populations that are most affected by the disease,” Montez Rath said.