By Aneri Pattani, Kaiser Health News
For a term that is at least 100 years old, “herd immunity” received new life in 2020.
It made headlines over the past month when reports surfaced that a White House Coronavirus Task Force member and adviser to the President, Dr. Scott Atlas, recommended it as a strategy to fight COVID-19. The Washington Post reported that Atlas, a health policy expert from Stanford University’s Hoover Institution, suggested spreading the virus among the population so that people could build immunity rather than try to contain it through shutdown measures.
At an event at City Hall a few weeks later, President Donald Trump himself brought the idea up and said the coronavirus would simply “go away” as people developed a “herd mentality” – a slip that was nevertheless understood as a reference to the same concept.
And just last week, Senator Rand Paul (R-Ky.) Sparked a heated debate at a committee hearing when he suggested the decline in COVID cases in New York City was more likely to be due to the immunity of the herd or the community in the community Population as attributable to this is said to be public health measures such as wearing masks and social distancing. Dr. Anthony Fauci, the leading U.S. infectious disease official, reprimanded Paul, pointing out that only 22% of the city’s residents have COVID antibodies.
“If you believe 22% is herd immunity, you are alone with that,” Fauci told the senator.
All of this talk got us thinking: People seem pretty confused about herd immunity. What exactly does this mean and can it be used to fight COVID-19?
An insecure strategy with high costs
Herd immunity, also known as community or population immunity, refers to the point at which enough people are sufficiently resistant to a disease that an infectious agent is unlikely to spread from person to person. As a result, the entire community – including those who do not have immunity – will be protected.
People generally receive immunity in two ways: vaccination or infection. For most diseases in recent history – from smallpox and polio to diphtheria and rubella – vaccines have been the route to herd immunity. The most contagious diseases like measles require about 94% of the population to be immunized to achieve this level of protection. For COVID-19, scientists estimate that the percentage is between 50% and 70%.
Prior to the COVID pandemic, experts cannot recall examples where governments deliberately turned to natural infections in an attempt to achieve herd immunity. In general, such a strategy could lead to widespread disease and death, said Dr. Carlos del Rio, an infectious disease and vaccine expert at Emory University School of Medicine.
“It’s a terrible idea,” said del Rio. “It basically gives up public health.”
A new, large study found that fewer than one in ten Americans have antibodies to SARS-CoV-2, the virus that causes COVID-19. Even in the hardest hit areas like New York City, residents’ estimated immunity is around 25%.
Achieving immunity of 50% to 70% would mean about four times as many people will be infected and an “incredible number of deaths,” said Josh Michaud, assistant director of global health at KFF. Even those who survive could have serious consequences for their heart, brain, and other organs that may have lifelong disabilities (KHN is an editorially independent program of the KFF.)
“It is not a strategy to pursue unless your goal is to pursue suffering and death,” Michaud said.
Additionally, some scientists say that natural immunity to COVID-19 may not even be feasible. While most people are believed to gain some protection after a single infection, cases of people who have recovered from the disease and been re-infected have raised questions about how long natural immunity lasts and whether someone with immunity can still spread the virus .
Even the way scientists use to measure immunity – blood tests to detect antibodies to the coronavirus – may not be an accurate indicator of who is protected against COVID-19, said Dr. Stuart Ray, an infectious disease expert at the Johns Hopkins University School of Medicine.
With so many unanswered questions, he concluded, “We cannot rely on natural herd immunity to control this epidemic.”
On the other hand, vaccines can be made to elicit stronger immunity than a natural infection, Ray said. Therefore, people who have a natural tetanus infection, for example, are still recommended to receive the tetanus vaccine. The hope is that vaccines being developed for COVID-19 will offer the same higher levels of immunity.
But what about Sweden?
In the political debate surrounding COVID-19, proponents of a natural herd immunity strategy often refer to Sweden as a role model. Although the Scandinavian country has taken fewer measures to shut down the economy, its death rate is lower than the US, Paul said at the Senate hearing on Wednesday.
But health experts – including Fauci during the same hearing – argue that this is a flawed comparison. The U.S. has a much more diverse population, with at-risk groups like black and Hispanic Americans disproportionately affected by the coronavirus, said Dr. Jon Andrus, epidemiology expert at the Milken Institute School of Public Health at George Washington University. The US also has greater population density, particularly on the coasts, he said.
Compared to other Scandinavian countries, the death toll in Sweden is much higher. There have been 5,880 COVID-19-related deaths to date, according to the Johns Hopkins University. That’s nearly 58 deaths per 100,000 people – a multiple of the death rate of 5 or 6 per 100,000 in Norway and Finland. Indeed, as a result of COVID-19, Sweden has recorded the highest death toll since a famine 150 years ago. And cases are on the rise.
Despite this level of losses, it is still unclear whether Sweden has reached the herd immunity threshold. A study by the country’s health department found that by the end of April, only 7% of Stockholm’s residents had antibodies to COVID-19. In other Swedish cities the percentage was even lower.
These results mirror other studies around the world. Researchers reported that in several cities in Spain, Switzerland and the United States – with the exception of New York City – less than 10% of the population had COVID-19 antibodies by June, despite months of exposure and high infection rates. The results prompted commentators in The Lancet medical research journal to write, “In light of these findings, any proposed approach to achieving herd immunity from natural infections is not only highly unethical, but also unattainable.”
Herd immunity is still a long way off
Natural herd immunity is an uncertain strategy, according to medical experts, and attempts to track it could result in a number of unnecessary deaths. A vaccine, once available, would offer a safer route to community-wide protection.
Until then, they emphasize that there is still a lot to be done to counter the pandemic. Wearing masks, practicing social distancing, washing hands and ramping up tests, and tracking down contacts have all been found helpful in curbing the spread of the virus.
“As we wait for new tools to be added to the toolbox,” said Andrus, “we have to keep reminding ourselves that at this moment there are measures that we could take to save lives.”
KHN reporter Victoria Knight contributed to this article.
KHN (Kaiser Health News) is a non-profit health news service. It is an editorially independent program of the KFF (Kaiser Family Foundation) that is not affiliated with Kaiser Permanente.