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 Not surprisingly, Israel has withdrawn recommendations and mandates for most nonpharmaceutical interventions like masks and social distancing.