Without a vaccine for coronavirus, could herd immunity ultimately be what protects the population in the days ahead? According to one University of Washington professor, we should be skeptical of any such approach.

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UW biology professor Carl Bergstrom points a handful of factors that not only indicate herd immunity isn’t a viable solution, but also potentially a “disastrous” method of quelling the spread of the virus.

“Given the uncertainties we face around the degree and duration of acquired immunity, it is not even clear that one could reach herd immunity for (COVID-19),” he said on Twitter. “But even if one could, the cost in lives would be unacceptable.”

There’s still quite a bit we don’t know about the immunity of individuals who have recovered from the virus, with antibody blood testing only recently having begun ramping up. As for herd immunity, Bergstrom points out, there’s no way to achieve that without a sizable death toll among the population.

Overall, that makes it “a disastrous control strategy for this pandemic,” not just in death toll, but in a total number of infections that would far exceed what it takes achieve that kind of immunity.

“If herd immunity requires 60% of the population to be infected, you can’t just let the epidemic go unchecked and expect to suffer ‘only’ 60% infected,” he cautioned.

That’s due to a concept known as overshoot, “whereby an epidemic infects more people that are required for herd immunity.”

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Because of that, even in a model where almost two-thirds of the population gets infected, we can expect an even higher number of infections, since the virus doesn’t simply stop spreading altogether after reaching that threshold.

“It takes place because an epidemic has something akin to momentum, in the form of people who are already infected when you reach the herd immunity threshold,” Bergstrom described. “An epidemic couldn’t start anew from that place, but the current one can keep going.”

Between that and what would be a massive death toll, it’s a strategy that could have fatal consequences, he argues.

“The cost in lives makes this approach untenable,” Bergstrom concluded.