The idea of “herd immunity” against Covid-19 has reached an almost magical status in the popular imagination. Once we reach that limit, many Americans believe, we will be free and the pandemic will finally disappear from history.
But it is unlikely that we will ever achieve collective immunity with Covid-19 – this is not how this nightmare will end. Although the case count is decreasing in relation to the winter peak, we fear another peak of potential over-spreading events after spring break, Easter weekend, Memory Day and 4th of July, or even again after the holidays. year-end. The time to double our efforts to eliminate transmission is now. We must develop what amounts to a national immune system to quickly detect and repel the new outbreaks that lie ahead, not only for this pandemic, but also for future ones.
Herd immunity is achieved when the percentage of a given immune population, 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 infection, begins to die.
The limit for herd immunity 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.
At the time 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, there have been about 30 million reported cases of Covid. Epidemiologists at CDC and NIH estimate that perhaps an equal number of cases, about 30 million, have not been reported.