They point to several factors making herd immunity for COVID-19 more aspirational than possible.

What does immunity mean? – We might have imagined that it was total; once treated, no infections. But breakthrough infections from the vaccine and reinfections from those with prior COVID-19 infections put that idea to rest. Immunity at this juncture is from severe disease – the disease trajectories that result in hospitalization or death. It is not immunity from being infected or being a transmitter to another.

Immunity, unlike herpes, is not forever – The protection afforded by our immune system varies with the foreign agent. It is basically one and done for measles, but for COVID-19 and other respiratory viruses like influenza, immunity wanes over time – an interval that varies with both the host and pathogen.

COVID-19, like the other respiratory viruses, is subject to antigenic drift – That is the term for what causes all the variants we have seen and will see. The shape-shifting of the virus may evade our immunity to a greater or lesser degree. In the dance between the virus and the host, the virus leads, and we follow. Pathogens with less antigenic drift, again measles comes to mind, is a target that remains relatively stationary. For COVID-19, in the words of the great epidemiologist Jerry Lee Lewis, there’s a “Whole lot of shakin’ goin’ on.”