The idea of ”herd immunity” against Covid-19 has reached almost magical status in the popular imagination. Once we reach that threshold, many Americans believe, we will go free and the pandemic will finally fade into history.
But it is unlikely that we will achieve herd immunity with Covid-19; This is not how this nightmare will end. Although the case count is now declining from its winter peak, we fear another spike of potential super spreader events after Spring Break, Easter weekend, Memorial Day, and July 4, or even again after the end of the year holidays. The time to redouble our efforts to end broadcasting is now. We must develop what amounts to a national immune system to quickly detect and repel the new outbreaks that are coming, not only for this pandemic but also for future ones.
Herd immunity is achieved when the percentage of a given population that is immune, through vaccination or previous infection, becomes such that each infected person transmits the disease to an average of less than one new case. The virus, finding an inadequate number of people susceptible to infect, begins to die out.
The herd immunity threshold depends on the contagiousness of a given disease. For Covid-19, the best estimates suggest that at least 80% of people would need to be immune.
As of this writing, 130 million doses of vaccine have been administered in the US, leaving 46.4 million fully immunized Americans and 33 million partially immunized while they await a second dose. In addition, around 30 million cases of Covid have been reported. Epidemiologists at the CDC and NIH estimate that perhaps an equal number of cases, some 30 million, have gone unreported.