Since the start of the Covid pandemic, CDC guidelines for preventing the spread of influenza have guided the public health response and communications. The approach starts with nonpharmaceutical interventions like facial coverings, social distancing, school closures, and limits on congregating. The next step is to add pharmaceutical interventions—especially vaccines—that reduce the number of cases and deaths, create herd immunity, and reduce spread of the virus almost to zero, followed by withdrawal of nonpharmaceutical interventions and a resumption of pre-pandemic normal life.
All this sounds simple in the abstract, but it is anything but that in practice. Complicating factors include questions like where personal choice ends and restrictive public health policy begins; the relationship between herd immunity and resumption of in-person gatherings at schools, restaurants, and other social functions; and how to communicate a realistic vision of post-pandemic life. At the center of all these issues is the argument about where the tipping point exists for compromising personal liberty to protect others.
To better understand this issue, let’s look at herd immunity and withdrawal of nonpharmaceutical interventions. Regardless of how it arises, whether from mass vaccination or recovery from prior infection, herd immunity is not defined by the percentage of the population that is immune. Rather, it means the virus is less likely to infect those without immunity because the immunized block its spread. For example, in Israel, where, as of late February, half the population was fully immunized or had recovered, the number of new infections created by a single infection had dropped below one. Further, the number of deaths had dropped considerably. Not surprisingly, Israel has withdrawn recommendations and mandates for most nonpharmaceutical interventions like masks and social distancing.
Several questions arise here that apply to our discussion of tipping points. What rights do individuals have to reject the vaccine? What is the responsibility of the herd to protect those who reject the vaccine? What are the costs to society of the unimmunized becoming infected and spreading infection? How do we balance these factors against personal choice?
Taking the first two questions together, if a sizable minority of the U.S. population freely chooses not to be vaccinated and has not developed immunity through infection, then the herd does not have a responsibility to protect them. The goal of mass vaccination thus should not be high levels of herd immunity but personal protection. Everyone should be free to make his own decision and to deal with the medical and nonmedical consequences.
A society might want to slow the spread for other reasons, even with high levels of herd immunity. There would still be a danger, for example, that new, highly contagious, and more lethal variants of the virus could develop. There’s still an important discussion to be had about whether the consequences of ongoing, albeit reduced, infection are severe enough to keep in place recommendations for nonpharmaceutical interventions, especially when considering the social, economic, and mental-health impact of the interventions and their impact on personal choice.
CDC guidelines and many public health officials put too much emphasis on determining a true end to the pandemic. Instead, they ought to be preparing society for a new, post-pandemic equilibrium. In this scenario, though vaccination rates would be relatively high, some would choose not to be vaccinated. There would be some herd immunity, but not at a sufficient level to stop the spread of Covid and its variants altogether. The consequences of the continuing spread would ebb and flow, and wearing a mask, avoiding gatherings, and sending children to school would become an individual choice, not a public health mandate or guidance.
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