Only 10% of US adults may have COVID-19 antibodies: Study

More than 90% of U.S. adults remain susceptible to COVID-19, according to research published on Friday.

Using data from dialysis centers in the United States, the study, published in The Lancet, estimates that less than 10% of U.S. adults have virus antibodies, meaning everyone else is potentially vulnerable to infection.

Those figures roughly match those of a forthcoming Centers of Disease Control and Prevention study, according to CDC Director Dr. Robert Redfield, who spoke at a Senate hearing on Wednesday.

"The preliminary results in the first round show that a majority of our nation, more than 90% of the population, remains susceptible," said Redfield, referring to an ongoing CDC study assessing the prevalence of antibodies to better track how widely the virus has spread.

CDC data from that study is expected to be published in the "next week or so," Redfield added.

The Lancet study offers new details about the prevalence of COVID-19. Researchers at Stanford University studied 28,503 U.S. patients receiving dialysis in July 2020 and found that 8% of those sampled had COVID-19 antibodies -- 9.3% when standardized to the general U.S. adult population.

The study raises questions over "herd immunity," the idea that when enough a large enough population becomes immune the virus could die off. One big problem, experts have said, is that they don't yet know enough about how immunity to COVID-19 develops to say whether antibodies provide adequate protection from reinfection.

"What we know about antibodies is that things get a little dicey," said Dr. Jay Bhatt, an ABC News contributor and former chief medical officer of the American Hospital Association. "People don't have a uniformly consistent or strong antibody response, so the question is, 'Can we achieve herd immunity with this particular virus, or will that not be possible?'"

The results provide "yet another data point that helps us reinforce that there are significant amounts of people in this country that haven't been exposed to the virus," Bhatt added. "This study suggests that we have a long way to go to get to the kind of immunity we need to move past the virus."

This study is different from many others in that it looked at dialysis patients, who already undergo routine, monthly laboratory studies. This allows for better and more reliable data collection.

Dialysis cleans the blood of patients with end-stage kidney disease. Because dialysis patients are from a diverse range of backgrounds, ethnicities and socioeconomic statuses, the group studied is a reasonable approximation for the rest of the country, the researchers said.

John Brownstein, an ABC News contributor and epidemiologist at Boston Children's Hospital, said the study's findings should be taken with a grain of salt as dialysis patients aren't necessarily representative of the general population.

Because dialysis patients are less likely to be employed and many have issues with mobility, they also could have been exposed to COVID-19 at lower rates, which would mean the actual number of people with antibodies has been underestimated. Or conversely, individuals on dialysis may be more susceptible to the virus because of chronic underlying health issues, meaning the number of those with antibodies has been overestimated.

Patients with end-stage kidney disease and patients with severe COVID-19 have several risk factors in common: they're older, have higher rates of hypertension and diabetes, and people of color are disproportionately affected by both. This adds an extra layer of insight to the study's findings.

"Being able to understand the level of vulnerability of the part of the population that is going to be most impacted by the virus is important," Brownstein said. "And understanding where they are at in terms of immunity or potential immunity is valuable information."

Leah Croll, M.D., a neurology resident at NYU Langone Health, is a contributor to the ABC News Medical Unit.