The idea of ”herd immunity” against Covid-19 has reached an almost magical status in the popular imagination. Once we reach the threshold, many Americans believe, we will be clear and the pandemic will finally go down in history.
But it’s unlikely we’ll ever reach the herd’s immunity with Covid-19 – that’s not how this nightmare will end. Although the number of cases has been declining since the peak of winter, we fear another increase in potential super-widespread events after the spring break, Easter weekend, Memorial Day and July 4, or even again after the holidays. end of the year. It is time to redouble our efforts to eliminate transmission. We need to develop what a national immune system means to quickly detect and reject new outbreaks in the future, not only for this pandemic, but also for future ones.
Immunity of the herd is obtained when the percentage of a given population that is immune, from vaccination or previous infection, becomes such that each infected person transmits the disease on average less than one new case. The virus, finding an inadequate number of people susceptible to infection, then begins to disappear.
The threshold for herd immunity depends on the contagion of a given disease. For Covid-19, the best estimates suggest that at least 80% of people should be immune.
As of this writing, 130 million doses of the vaccine have been administered in the United States, leaving 46.4 million Americans fully immunized and 33 million partially immunized while awaiting a second dose. In addition, approximately 30 million cases of Covid have been reported. Epidemiologists at the CDC and NIH estimate that perhaps an equal number of cases, about 30 million, remained undeclared.