Herd Immunity: What the Science Says About Letting COVID Spread Freely

As the coronavirus that causes COVID-19 continues to spread around the world, an approach to preventing the spread of infectious disease known as herd immunity has sparked debate.

Usually, the term herd immunity refers to using vaccines to ensure a significant proportion of a population is protected for an infectious disease and can't spread it. That is how measles was eliminated in the U.S. 20 years ago, for instance, although a drop in vaccination rates has led to outbreaks in recent years.

Herd immunity has taken on a different meaning amid the COVID-19 pandemic, as there are currently no vaccines to protect against the coronavirus, although dozens are being developed around the world. Some have controversially argued that lockdowns should be abandoned and immunity should be gained by allowing the virus to spread in the general population, while the most vulnerable are protected.

Scientists writing in the journal Nature Reviews Immunology estimated that "there is little evidence" to suggest the coronavirus might stop spreading naturally in a population before at least 50 percent has become immune. "Assuming an optimistic herd immunity threshold of 50%, for countries such as France and the USA, this would translate into 100,000–450,000 and 500,000–2,100,000 deaths, respectively," wrote epidemiologist Arnaud Fontanet and Simon Cauchemez, head of the Mathematical Modelling of Infectious Diseases Unit, both of France's Institut Pasteur.

Francis Collins, the director of the National Institutes of Health, told The Washington Post, he was worried the idea is being presented as a "a major alternative view" held by a large number of experts in the scientific community. Collins said that's not true, and described the idea as "fringe" and "not mainstream science."

After largely being associated with discussions around policies in the U.K. and Sweden earlier in the pandemic, the debate around herd immunity was reignited last week with the signing of the Great Barrington Declaration. The authors argue that lockdowns have had "devastating effects" on public health. Instead, they believe that herd immunity should be reached by allowing those least likely to be killed by the virus to return to normal life, and the vulnerable protected.

Its authors—who signed the document at the libertarian think-tank, the American Institute for Economic Research—include Martin Kulldorff, professor of medicine at Harvard University, Sunetra Gupta, professor of theoretical epidemiology at Oxford University, and Jay Bhattacharya, professor of medicine at Stanford University Medical School.

Last week, Secretary of Health and Human Services Alex Azar said he and Trump administration coronavirus advisor Scott Atlas met with Kulldorff, Gupta and Bhattacharya.

Reports citing unnamed officials, including from The Washington Post, indicate that Atlas is promoting herd immunity in the White House. Atlas has previously denied this. Newsweek has contacted the White House and Atlas for comment.

Last week, Atlas appeared to refer to the three scientists in a written statement to Newsweek about the White House's COVID-19 response, stating: "To combat the pandemic, this administration is focused on a strategy that is now being endorsed by epidemiologists and top scientists across the political spectrum from Harvard, Stanford, and Oxford among other elite research and medical science institutions: 1) protecting the vulnerable, 2) preventing hospital overcrowding, and 3) reopening schools and society."

According to the declaration's website, over 9,500 "medical & public health scientists" and 25,048 "medical practitioners" have signed the letter, although U.K. news outlet Sky News revealed last week that fake names had appeared in the list last week, with experts including "Dr Johnny Bananas."

Bhattacharya told Newsweek he understands there was a "dishonourable campaign" by what he described as "lockdown proponents" to add fake signatures to the letter. The site's hosts have been working to remove the names that make up fewer than 1 percent of signatories, according to Bhattacharya.

Last week, a separate team of researchers based at the University of Edinburgh School of Physics and Astronomy published a study in the journal BMJ based on a simulated country with parallels to the UK population. By running different scenarios of response to the pandemic through the model, they found that closing schools and universities may increase the number of deaths when compared with not doing so, as this may prolong the pandemic, leading to more older and vulnerable people dying in the long term. An opinion piece on the study by scientists not involved in the paper said the research did not take into account the long-term effects of COVID-19.

Studies show that lockdowns have been effective for preventing the spread of the coronavirus and saving lives. The authors of a paper published in the journal Science in April concluded that measures China put in place at the start of the COVID-19 pandemic may have prevented 700,000 infections. Earlier this week, Professor Dame Anne Johnson vice president at the Academy of Medical Sciences, told Newsweek there is no doubt lockdown measures were able to "dramatically suppress the amount of transmission."

Last month, Independent Sage, a group of scientists lead by Sir David King, former chief scientific adviser to the U.K. government, published a report on why herd immunity would not work, stating it is "not only unlikely to achieve the desired objective of population immunity, but risks a significant amount of avoidable death and illness, without protecting the economy."

On Monday, World Health Organization (WHO) Director-General Tedros Adhanom Ghebreyesus told a press conference: "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."

Tedros said that when herd immunity is achieved with vaccines, it is achieved by "protecting people from a virus, not by exposing them to it." Not enough is known about the strength and length of person's immunity after catching the coronavirus, and how it differs from person to person. There have also been examples of people being infected for a second time, he said.

The WHO director general went on that less than 10 percent of the global population has been infected with the coronavirus. According to Johns Hopkins University, over 38.1 million people are known to have been infected with the coronavirus, and over 1 million have died. The U.S. is the country with the highest case and death tolls, at 7.8 million, and almost 216,000, respectively.

"Letting the virus circulate unchecked therefore means allowing unnecessary infections, suffering and death," he said. And although older people and those with underlying health conditions are most at risk of severe COVID-19 and death, people of all ages have died, and the long-term health impacts are poorly understood. For instance, some previously fit and healthy individuals have reported suffering from "long COVID."

"Allowing a dangerous virus that we don't fully understand to run free is simply unethical. It's not an option," said Tedros. His concerns echoed those of fellow WHO officials.

Tedros said the choice isn't between letting the or shutting down society, but using the tools the organization has been advocating for from the start: tracking, testing, isolating, and caring for cases, and tracing and quarantining their contacts.

Stephen Griffin, associate professor in the School of Medicine at the U.K.'s University of Leeds, said in a statement: "scientifically, no evidence from our current understanding of this virus and how we respond to it in any way suggests that herd immunity would be achievable, even if a high proportion of the population were to become infected."

He said: "We are all exhausted by the pandemic and are rightly angry at the notion of potentially enduring a second round of local and national lockdowns or other restrictions. However, we must not conflate the failures of certain governments to capitalize upon the sacrifices people make during lockdowns with these measures themselves being ineffective."

Echoing his concerns, Simon Clarke, associate professor of cellular microbiology at the University of Reading, U.K., said in a statement: "There is no current evidence about COVID-19 to suggest that a long-term passive approach has any merit."

Michael Head, senior research fellow in global health at the U.K.'s University of Southampton, said the declaration is based on a "false premise" that governments and the scientific community wish for extensive lockdowns to continue until a vaccine is available.

Head said "the idea being that somehow the vulnerable of society will be protected from ensuing transmission of a dangerous virus. It is a very bad idea." He gave the example of the U.K. that even with intensive lockdowns in place, there was a "huge death toll," mainly among the elderly, with 20 to 30 percent of the UK population classed as vulnerable to severe COVID-19.

Countries such as South Korea and New Zealand, "who are managing the pandemic relatively well" according to Head, do have not been "simply letting the virus run wild whilst hoping that the asthmatic community and the elderly can find somewhere to hide for 12 months."

Rupert Beale, group leader in the Cell Biology of Infection Laboratory at the U.K.'s Francis Crick Institute, said in a statement that multiple targeted interventions are needed to respond to the pandemic, including reducing the spread, developing better treatments, and protecting the vulnerable.

The Great Barrington Declaration "prioritizes just one aspect of a sensible strategy—protecting the vulnerable—and suggests we can safely build up 'herd immunity' in the rest of the population. This is wishful thinking." Beale said it's not possible to fully identify vulnerable individuals, or fully isolate them.

As immunity to other members of the coronavirus family of viruses herd immunity would likely not be possible without a vaccine, said Beale. Immunity is known to fade for the common cold as well as MERS and SARS.

Bhattacharya told Newsweek: "it is true that current policies, which require "'essential' workers and the poor to be put in situations where they may be exposed, do not protect the vulnerable. It is also true that many places under the general lockdowns have failed to protect nursing home residents from exposure to the virus. It is also true that current policies provide no provision for elderly people living in multi-generational homes to be shielded should a family member be exposed to the virus. The declaration provides concrete ideas to use our resources to fix those problems."

This article has been updated with comment from Jay Bhattacharya.

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A stock image shows a group of people wearing masks. A group of scientists has proposed the idea of letting the coronavirus spread among populations while protecting the vulnerable. Getty