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Oct. 28, 2020, 10:15 a.m. EDT

Targeting herd immunity from COVID-19 without a vaccine remains a deadly idea — here’s why

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By Steven Albert

White House advisers have made the case recently for a “natural” approach to herd immunity as a way to reduce the need for  public health measures to control the SARS-CoV-2 pandemic while still keeping people safe. This idea is summed up in something called the  Great Barrington Declaration , a proposal put out by the  American Institute for Economic Research , a libertarian think tank.

The basic idea behind this proposal is to let low-risk people in the U.S. socialize and naturally become infected with the coronavirus, while vulnerable people would maintain social distancing and continue to shelter in place. Proponents of this strategy claim so-called “natural herd immunity” will emerge and minimize harm from SARS-CoV-2 (and the COVID-19 disease it causes) while protecting the economy.

Another way to get to herd immunity is through mass vaccinations, as we have done with measles, smallpox and largely with polio.

A population has achieved herd immunity when a large enough percentage of individuals become immune to a disease. When this happens, infected people are no longer able to transmit the disease, and the epidemic will burn out.

As a professor of  behavioral and community health sciences , I am acutely aware that mental, social and economic health are important for a person to thrive, and that public health measures such as social distancing have imposed severe restrictions on daily life. But based on all the research and science available, the leadership at the University of Pittsburgh Graduate School of Public Health and I believe this infection-based approach would almost certainly fail.

Dropping social distancing and mask wearing, reopening restaurants and allowing large gatherings will result in overwhelmed hospital systems and skyrocketing mortality. Furthermore, according to recent research, this reckless approach is  unlikely to even produce the herd immunity  that’s the whole point of such a plan.

Vaccination, in comparison, offers a much safer and likely more effective approach.

Herd immunity is an effective way to limit a deadly epidemic, but it requires a huge number of people to be immune.

The proportion of the population required for herd immunity depends on how infectious a virus is. This is measured by the  basic reproduction number, R0 , how many people a single contagious person would infect in a susceptible population. For SARS-CoV-2,  R0 is between 2 and 3.2 . At that level of infectiousness, between 50% and 67% of the population would need to develop immunity through exposure or vaccination to contain the pandemic.

The Great Barrington Declaration suggests the U.S. should aim for this immune threshold through infection rather than vaccination.

To get to 60% immunity in the U.S., about 198 million individuals would need to be infected, survive and develop resistance to the coronavirus. The demand on hospital care from infections would be overwhelming. And according to the  WHO estimated infection fatality rate of 0.5% , that would mean nearly a million deaths if the country were to open up fully.

The Great Barrington Declaration hinges on the idea that you can effectively keep healthy, infected people away from those who are at higher risk. According to this plan, if only healthy people are exposed to the virus, then the U.S. could get to herd immunity and avoid mass deaths. This may sound reasonable, but in the real world with this particular virus, such a plan is simply not possible and ignores the risks to vulnerable people, young and old.

Read: Lilly signs deal with U.S. government for still-investigational COVID-19 antibody drug

The  Great Barrington Declaration  calls for “allowing those who are at minimal risk of death to live their lives normally … while protecting those who are at highest risk.” Yet healthy people can get sick, and asymptomatic transmission, inadequate testing and difficulty isolating vulnerable people pose severe challenges to a neat separation based on risk.

First, the plan wrongly assumes that all healthy people can survive a coronavirus infection. Though at-risk groups do worse, young healthy people are  also dying  and  facing long-term issues from the illness.

Second, not all high-risk people can self-isolate. In some areas, as much as  22% of the population have two or more chronic conditions  that put them at higher risk for severe COVID-19. They might live with someone in the low-risk group and they still must shop, work and do the other activities necessary for life. High-risk individuals will come in contact with the low-risk group.

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