During the spring 2020 COVID wave, it’s likely that we were diagnosing only about one out of every ten or fifteen actual infections. With more testing in place, by the summer, that proportion improved to about one in eight infections, and by the fall, one in four. Thus, even thousands of cases lurking in a large city might not be enough infection to generate an identifiable signal of disease, especially because it was late winter, and the virus was able to hide in the shadow of flu season.
