The coronavirus moved so rapidly across the globe partly because no one had prior immunity to it. Failure to check its spread will result in a catastrophic loss of lives. Yet some politicians, epidemiologists and commentators are advising that the most practical course of action is to manage infections while allowing so-called herd immunity to build.
The concept of herd immunity is typically described in the context of a vaccine. When enough people are vaccinated, a pathogen cannot spread easily through the population. If you are infected with measles but everyone you interact with has been vaccinated, transmission will be stopped in its tracks.
Vaccination levels must stay above a threshold that depends upon the transmissibility of the pathogen. We don’t yet know exactly how transmissible the coronavirus is, but say each person infects an average of three others. That would mean nearly two-thirds of the population would need to be immune to confer herd immunity. Continue reading.