"Asymptomatic" was used as early as the (fake?) polio epidemic. I remember the word from "The Moth in the Iron Lung", which I read near the end of the WuFlu time. At least the author, Forrest Maready, named it such. The book is from 2018. p. 64 Eventually, physicians began to believe that for every person who developed poliomyelitis, many others had developed the viral infection responsible for it—without showing any paralysis, possibly without presenting any symptoms of sickness at all. These asymptomatic carriers were thought to be the missing link in the fractured outbreak maps and the method by which the virus was traveling. p. 132 Their options to contain it were pitifully few. Isolation and quarantine would be strictly enforced, but with so many asymptomatic carriers of disease on the loose, these draconian separations were more for show than anything. p. 154 More than a few scientists held onto the idea that the poliovirus was spread chiefly through the excreted stool of persons infected—asymptomatic or otherwise —and assumed that the poliovirus would eventually be shown to be spread by flies. Google Trends seems not to be working for me atm. That might give some more insight.