Why Herd Immunity Is a Bad Public Health Policy

Scientists in a top medical journal warn that herd immunity is ‘fraught with risks’

Photo: De an Sun on Unsplash

Herd immunity has reentered the national coronavirus conversation, this time because of a controversial document, endorsed by President Trump, known as the Great Barrington Declaration. Published on October 4 and written by a trio of scientists, this document calls for an end to lockdowns, the reopening of businesses and schools, and increased reliance on the concept of herd immunity: the concept that a virus can’t spread as easily if a sufficient proportion of the population is immune.

The basic concept behind the Great Barrington Declaration is that people at high risk of being vulnerable to Covid-19 should be sequestered while everyone else should be allowed to live life normally. The latter group very well could get Covid-19, but the hope is that they’d be more likely to recover and thus gain immunity, and eventually enough people will have immunity (a proportion of people known as the “herd immunity threshold”) that the virus will no longer be able to spread. This way, the authors argue, nationwide lockdowns will no longer be necessary. It’s obvious why this theory appealed to the White House, which has refused to impose national lockdowns even when scientists said they were a necessary emergency measure.

Numerous experts have vehemently pushed back on this approach, citing a multitude of factors that must be met (and likely won’t) for herd immunity to work. Eighty scientists criticized the herd immunity approach in the Lancet last week, and on Monday, a group of scientists led by Saad B. Omer, PhD, of the Yale Institute of Global Public Health, detailed its shortcomings in the medical journal JAMA. Such a strategy, they write, “is fraught with risks.” The authors point to a few key ones:

Mortality will still be high

Even if the most high-risk people are sequestered to protect them from getting Covid-19, creating conditions where low-risk people can freely get infected will still result in high mortality. The reason is simple: The vast majority of people are not immune to Covid-19. Even if Covid-19 had a modest infection fatality rate (World Health Organization estimates put it at 0.5%), if a large population got infected, a substantial number of people would die. According to the authors’ calculations, 190 million of the 330 million people in the United States would need to be immune to reach a herd immunity threshold of 60%, which, the authors write, would result in “several hundred thousand additional deaths.” More than 200,000 people have already died from Covid-19 in the United States.

Sequestering high-risk people won’t keep them safe

The Great Barrington document states that protection should be given to the most vulnerable, notably the elderly. It doesn’t, however, include a plan for how to keep these people safe from everyone else who is potentially exposed to or infected with Covid-19. For example, if an elderly person lives in a multigenerational household, where younger family members have been living life as normal, how are they supposed to avoid infection?

There’s no proof that it works on this scale

So far, the authors write, “there is no example of a large-scale successful intentional infection-based herd immunity strategy.” (Note that this is different from a vaccine-based herd immunity strategy, which does work, albeit imperfectly.) Sweden is the most obvious example of a country that tried to go for herd immunity as public policy, and doing so resulted in some of the world’s highest death rates (especially among the elderly) and economic losses comparable to other European countries, as the New York Times noted in its coverage of the Great Barrington document. And though one might expect many people in Sweden to have antibodies against Covid-19 after this strategy was adopted, the so-called seroprevalence in Stockholm, Sweden, was reported as less than 8% in April — about the same as other cities.

It’s not known how long immunity lasts

Sustained herd immunity requires that individuals are immune to the coronavirus for a long period of time. It’s not yet clear how long immunity to the coronavirus lasts, and reinfection with the virus has been documented in a few cases.

It’s easy to understand why a plan that calls for an end to lockdowns has great appeal. After seven months of pandemic-induced restrictions, pandemic fatigue is setting in, and people are desperate to return to normal life. But risking the additional deaths of hundreds of thousands of Americans — many of whom are likely to be poor and people of color — in order for a majority of people to do so is unacceptable, no matter how dire anyone’s individual situation may be.

Experts who spoke to the New York Times reminded us that lockdowns are only an emergency response to Covid-19 outbreaks (like the United States is experiencing now) and are by no means the only strategy available for tamping down its spread. Universal masking, social distancing, and test-and-trace strategies, said David Nabarro, MD, a special envoy to the World Health Organization, are all proven ways to help control outbreaks without having to resort to lockdowns. If enough people, with the proper encouragement from the government, could get behind these strategies, there would be no reason to pin our hopes on a plan to end Covid-19’s spread that puts so many people’s lives in danger.

Editor, Medium Coronavirus Blog. Senior editor at Future Human by OneZero. Previously: science at Inverse, genetics at NYU.

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