The same dynamics that keep us safe in a pack, herd or society, and comfortable in our family, friends or neighbours also serves as a way for pathoge… - Chris von Csefalvay

The term 'natural immunity' has been often used to express post-infectious immunity and differentiate it from vaccine-induced immunity. In practice, this is not necessarily helpful. There is nothing fundamentally "unnatural" in vaccine-induced immunity, and while the minutiae of natural infection and vaccine-induced immunity might differ, this is a quintessentially unhelpful notion.

Despite the advances of modern medicine, the challenges of global epidemics have only become greater. Habitat loss of viral reservoir species increases the likelihood of zoonotic spillover events. Our global trade and transportation networks enable pathogens to make their way around the world in 24 hours. Climate change is disrupting fragile ecosystems and global poverty, especially urban poverty, exacerbates the problem.

The small town of Gunnison, Colorado, lies at the bottom of the valley carved by the Gunnison River into the Rocky Mountains. It is now crossed by the Colorado stretch of U.S. Highway 50, but in 1918 the town was mainly supplied by train and two at best mediocre roads. When the 1918–19 influenza pandemic reached Colorado as an unwelcome stowaway on a train carrying servicemen from Montana to Boulder, the town of Gunnison took decisive action. As the November 1, 1918, edition of the Gunnison News-Champion documents, a Dr. Rockefeller from the nearby town of Crested Butte was “given entire charge of both towns and county to enforce a quarantine against all the world”. He instituted a strict reverse quarantine regime that almost entirely isolated Gunnison from the rest of the world. Gunnison became one of the few communities that largely escaped the ravages of the influenza pandemic, at least in the beginning. In an instructive example of the limited human patience for the social, psychological, and economic disruption of quarantine, adherence eventually waned, and the front page of the Gunnison News-Champion’s March 14, 1919, issue reports that the influenza pandemic got to Gunnison, too Nevertheless, Gunnison had a very lucky escape, of a population of over 6900 (including the county), there were only a few cases and a single death.