As the United States enters the fall with schools still closed in many parts of the country and many businesses still forced to operate with significant restrictions, the idea of a “herd immunity” strategy for fighting the coronavirus is gaining some traction.
It’s easy to see the appeal of such an approach. Despite widespread and sustained lockdowns, the coronavirus has still spread in the U.S., with about 6 million infections and over 180,000 deaths. So, while the business-destroying restrictions have not prevented the virus from doing damage, the isolation has prevented a lot of people from developing natural immunity, not to mention all the other devastating societal impacts of the lockdowns.
The U.S., in a sense, is experiencing the worst of both worlds — too many deaths and too many restrictions.
Given that the virus poses much less danger to younger and healthier individuals, there is an argument that those populations should be encouraged to go about their business, while more precautions are taken for the older and more vulnerable populations. Simply waiting around for a vaccine would make the current lockdown strategy unsustainable if the vaccine ends up being years rather than months away.
This basic argument has a proponent in Scott Atlas, the Hoover Institution fellow and former chief of neuroradiology at Stanford University Medical Center, who recently became a coronavirus adviser to President Trump.
Despite the obvious attraction and logic behind the herd immunity strategy, there are several significant risks associated with it.
One is that it is likely to mean more infections and deaths, perhaps far more. Estimates of the proportion of the population required to achieve herd immunity have ranged from 20% to 70%. Even if the lower end is correct, that would mean 66 million infections in the U.S. At the higher end, it would mean 230 million. While there is considerable debate over the fatality rate of the coronavirus, this level of infection is likely to mean at least several hundred thousand more deaths and perhaps 2 million more. And that number does not take into account any sort of long-term health effects of those who survive.
This brings us to another issue, which is that infecting that many people will take a lot of time. In the past six months, there have been 6 million confirmed cases in the U.S. Though there have likely been many unconfirmed cases, even taking that into account, it would take many more months and perhaps years to achieve 66 million to 230 million infections. If the virus spreads more rapidly, leading to tens of millions of cases simultaneously, it would be the exact opposite of “flattening the curve” and would put a severe strain on the medical system.
It’s also not clear how older and more vulnerable people would be isolated from the younger population. Younger people interact with their older relatives, and the elderly rely on younger health workers for help. It’s difficult to see how we’d protect older people while allowing the virus to spread like wildfire through the rest of the population.
Let’s say, however, that the U.S. is willing to absorb the deaths and go through the long process of building up herd immunity. A big unknown is how long that immunity would last. There is considerable debate over cases in which individuals who had recovered with COVID-19 end up testing positive again. Were they truly reinfected? Never fully recovered? Or was it due to some of the imperfections in testing?
COVID-19 is still less than a year old, and there simply have not been enough cycles of it to assess how immunity works or how long it lasts. If people who recover from COVID-19 can remain immune for years, that’s one thing. But if they’re vulnerable again after six months, that’s quite another. If that were the case, by the time a large enough percentage of the population has been infected, those infected early will start to become vulnerable again.
Herd immunity, thus, is a huge gamble. In a world in which herd immunity can be achieved with just 20% of the population infected, the fatality rate is much lower than 1%, immunity lasts a long time, and the vaccine would otherwise be years away, it could be the best strategy. But it’s also possible that closer to 70% of the population needs to be infected, the fatality rate is closer to 1%, immunity is shorter-lived, and the early vaccines end up being effective and available by early next year, allowing us to achieve herd immunity more safely.
After six months of significant restrictions, it’s understandable that people are looking for an exit strategy. Public officials, with such actions as school closures, have veered well beyond the original argument for “flattening the curve.” And they have done themselves no favors by arbitrarily deciding what form of activities are too risky — for instance, thousands of people protesting is somehow seen as OK as long as they’re doing it for an accepted cause.
Yet even while acknowledging that, we should also be honest about the significant downside risk of a “herd immunity” strategy.