Fewer than 10 per cent of Americans have antibodies that could protect them from developing Covid-19, according to the first nationally representative survey that shows the vast majority still have not developed an immune response to the virus.
The serological survey, published in the medical journal The Lancet on Friday, also found that black and Hispanic communities had two to four times higher rates of antibodies to Sars-Cov-2, the virus that causes Covid-19, after they were hit harder by outbreaks earlier this year.
Julie Parsonnet, a professor of medicine at Stanford University and author of the study, said vulnerable populations would need to be protected until an effective vaccine is approved.
“This research clearly confirms that despite high rates of Covid-19 in the United States, the number of people with antibodies is still low and we haven’t come close to achieving herd immunity,” she said.
Higher rates of antibodies were found in the north-east, with New York state, the early epicentre of the virus in the US, having by far the most, at 21.5 per cent of the population. The west was the region with the lowest rates, between 3.6 and 4.9 per cent.
The study, conducted in July, comes as US public health leaders are pushing back against an argument from some allies of President Donald Trump that certain communities could be near herd immunity, the point at which a virus has difficulty spreading because so many people are immune.
Robert Redfield, director of the Centers for Disease Control and Prevention, told Congress on Wednesday that its data showed about 90 per cent of the population “remains susceptible”. He was later accused of using old data by Scott Atlas, a White House adviser on the coronavirus who is not an infectious disease specialist.
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It also follows a stand-off between Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, and Senator Rand Paul, at a recent congressional hearing. The Republican senator, who has criticised public health measures taken to stem the spread of the virus, said he believed New York was seeing lower rates of Covid-19 because it had achieved some level of herd immunity.
Citing data from a previous study in New York, Dr Fauci replied: “If you believe 22 per cent is herd immunity, I believe you’re alone in that.” The proportion required for herd immunity can range between 50 and 90 per cent, depending on the disease, according to Johns Hopkins.
The Lancet survey was conducted on more than 28,000 dialysis patients, who were easy to follow because they regularly have blood drawn and access to healthcare through Medicare. They also tend to be older and more likely to live in poverty, which have been identified as risk factors for Covid-19.
The study’s authors acknowledged there were some differences from the general population that could affect the figures: for example, they might be more exposed because they often take shared transportation to get to dialysis, or less exposed, because they were less likely to work.
Professor Barnaby Flower and Professor Christina Atchison, from Imperial College London, who were not involved in the study, praised it for finding a way to track antibodies across the country and over time, including the opportunity to improve the understanding of how long an immune response lasts.
In a comment also published in the journal, they said that “despite the massive burden of Covid-19 in the USA”, the study shows only a “small minority has immunity”.