By Sarah Toy & Daniela Hernandez

A group of scientists is pushing back on renewed calls for a herd-immunity approach to Covid-19, calling the method of managing viral outbreaks dangerous and unsupported by scientific evidence.

Eighty doctors and public-health and medical researchers called the herd-immunity approach a “dangerous fallacy” in a letter published Wednesday. The researchers noted that it is still unknown how long recovered patients might be immune from the virus. Since the letter was published, more than 2,000 others have signed it in a show of support.

This comes after White House officials outlined a federal strategy for dealing with the coronavirus in a call last week with journalists, pushing for a full reopening of society and citing a document written by three scientists that espouses immunity through natural infection.

Scott Atlas, a radiologist and one of the president’s coronavirus advisers, touted the document during a television interview Thursday. “We just had a declaration written and the thrust of the declaration is exactly aligned with the president, that is opening schools, opening society, and protecting the high-risk people, the seniors,” he said.

The document, called the Great Barrington Declaration, promotes an approach it calls “focused protection,” which pushes for young, healthy people to live life normally and get infected to build up immunity in the population, while working to better protect high-risk groups, such as the elderly and those with pre-existing conditions, like obesity and diabetes.

“As immunity builds in the population, the risk of infection to all—including the vulnerable—falls,” the document said. “We know that all populations will eventually reach herd immunity—i.e., the point at which the rate of new infections is stable—and that this can be assisted by (but is not dependent upon) a vaccine. Our goal should therefore be to minimize mortality and social harm until we reach herd immunity.”

Most scientists, including Anthony Fauci, the Trump administration’s top infectious-disease expert, say the strategy is flawed.

“Never in the history of public health has herd immunity been used as a strategy for responding to an outbreak, let alone a pandemic. It is scientifically and ethically problematic,” said World Health Organization director general Tedros Adhanom Ghebreyesus in an Oct. 12 tweet.

“There’s no debate here,” said Ashish Jha, dean of Brown University’s School of Public Health. “What they’re calling for would just lead to many—hundreds of thousands of Americans—dying.”

Several other prominent scientists have stated similar views, publicly denouncing the Great Barrington Declaration in interviews and on Twitter.

Despite publicly embracing the Great Barrington Declaration, Dr. Atlas in a statement denied he and the White House have ever advocated for achieving herd immunity through community spread.

“We emphatically deny that the White House, the President, the Administration, or anyone advising the President has pursued or advocated for any strategy of achieving herd immunity by letting the coronavirus infection spread through the community,” he said.

The three authors of the declaration met at the American Institute for Economic Research, a libertarian-leaning think tank in Great Barrington, Mass., to create a video discussing herd immunity and the Covid-19 pandemic, according to the document’s official website. The think tank supplied the means for them to record the video, the website said. Afterward, the authors decided to write a short document summarizing their thinking.

The authors of the document, which gets its name from where it was written and signed, include Martin Kulldorff, a professor of medicine at Harvard Medical School, and Jay Bhattacharya, a professor of medicine at Stanford University Medical School. The third, Sunetra Gupta, a professor of theoretical epidemiology at Oxford University, earlier this year garnered criticism for suggesting that some places might be able to reach herd immunity with just 25% of people infected, due to protection from previous exposure to seasonal coronaviruses

Most epidemiologists estimate it would take much more than that, between 50% and 70%, for a population to reach herd immunity. A study published in September found that less than 10% of 28,500 blood samples from dialysis patients across the U.S. tested positive for coronavirus antibodies.

The herd-immunity strategy the paper outlines hinges on separating those who are vulnerable from those who aren’t. In an email Dr. Bhattacharya said beefing up testing and providing personal protective equipment to vulnerable workers also are part of the focused-protection approach.

Scientists and public-health experts agree those are important elements of prevention, but they note that it would be impossible to identify and separate those who are vulnerable from the rest of society. In some regions, up to 30% of people have underlying conditions that make them susceptible to hospitalization and death from Covid-19, they say. And many older, more vulnerable people live in homes with their healthier children and grandchildren.

The U.K. sought such an approach early on in the pandemic. In March, the U.K. government’s chief scientific adviser said it would be impossible to prevent everyone from getting the disease and that acquiring some herd immunity would be important without a vaccine. The country quickly dropped that strategy after research by Imperial College in London showed that it would result in more than 500,000 deaths.

It is unknown how long immunity to the new coronavirus lasts and what level of antibodies is protective, infectious disease experts said. A handful of reinfection cases have been documented around the world, the first one in Hong Kong. Scientists last week reported the first confirmed U.S. reinfection case in a 25-year-old male patient in Nevada.

If immunity wanes after several months, as it does with the flu, patients could be susceptible to the virus after being infected, they said. That, they said, would result in recurrent and potentially large waves of infection, a common occurrence before vaccines were invented. That would continue to place a huge burden on the economy and health-care system, they said.

Allowing the virus to run its course could lead to thousands of people with long-term health problems, scientists say. Researchers are still trying to piece together who is most at risk for a condition known as “long Covid,” or lingering health issues that a significant proportion of Covid-19 patients experience weeks and months after they get sick. These patients struggle with issues ranging from problems with concentration, thinking and memory to extreme fatigue, and muscle and joint pain.

“We still don’t know all the consequences of being infected.” said Gavin Yamey, a physician and professor of global health and public policy at Duke University, who was one of the scientists who wrote the Lancet letter. “People with long Covid, some can’t work or play with their kids anymore. They can’t go up the stairs, they can’t do light exercise.”

The Lancet letter “mischaracterizes the focused protection approach advocated by the Great Barrington declaration, and vastly underplays what the scientific evidence is saying regarding the vast physical and mental harms of the lockdowns on people around the world, especially the poor,” said Dr. Bhattacharya in his email.

Some scientists note that the “focused protection” strategy also leaves out a key threat for those who are at risk of severe disease and death from Covid-19: asymptomatic people who can unwittingly transmit the virus to those around them, including the elderly and vulnerable.

Silent spread is the “Achilles heel” of Covid-19 prevention, said Abraar Karan, a global health physician at Brigham and Women’s Hospital and Harvard Medical School.

“We understand how easily and how invisibly the virus transmits,” he said. “It’s quite reckless for [the Trump administration] to embrace this declaration when for months and months they’ve been ignoring the advice of many of the mainstream thought leaders in epidemiology, infectious disease and virology.”

Dr. Karan and other experts say that silent transmission among those who don’t have symptoms has fed the runaway spread of cases that has at times led to increases in deaths or costly hospitalizations among at-risk populations.