Fewer than 1 in 10 Americans showed signs of past infection with the novel coronavirus as of late July, suggesting that most of the country may still be vulnerable to infection, according to one of the largest studies of its kind published Friday in the journal the Lancet.
That proportion is an estimate based on the percentage of dialysis patients whose immune systems produced coronavirus antibodies. It does not indicate exactly how many Americans may be immune to the virus, because not every infected individual develops antibodies. It is also unclear how strong a defense antibodies might confer or for how long. But, combined with similar results from studies by the Centers for Disease Control and Prevention and other institutions, it’s evident a large majority may not be protected against a disease that has already killed 200,000 Americans.
“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.
This means for every case diagnosed by a nasal or saliva swab in the country, about nine more people have antibodies for the coronavirus, the study estimated. Many people remain potentially at risk. “It basically does show that a minority of the U.S. population has evidence of antibodies to SARS-CoV-2 right now,” said study co-author Shuchi Anand, a nephrologist at Stanford University.
The findings also suggest herd immunity is far off without the advent of a vaccine. Epidemiological models suggest about 70 percent of the population would need to be protected from the coronavirus to make its spread unlikely, said study co-author Julie Parsonnet, an infectious-disease epidemiologist at Stanford University, acknowledging antibody studies are “not a perfect way” to track this. [Continue reading…]