In early 2020, it was assumed that most people who contracted Covid would fully recover in two to three weeks. Months later, we learned that a significant proportion of survivors are plagued by lingering symptoms that we now recognize as long Covid. In 2021, analyses of electronic health record data showed how Covid patients, especially those treated in hospitals, were at higher risk of a constellation of problems — from diabetes and depression to heart attacks and strokes — months later. The research, though, was based on observational data that linked or associated a SARS-CoV-2 infection with subsequent health effects. To test if the coronavirus actually causes a new health problem requires experimentally infecting people and comparing them with uninfected “controls.”
After a rigorous review of the ethics, UK researchers did precisely that in early 2021.
Their so-called human challenge study was the first — and likely only — research to involve inoculating healthy, young, unvaccinated adult volunteers with the original coronavirus strain. The research yielded unique and important insights into why some people manage to avoid infection and why others can spread it widely. But the latest finding might be the most eye-opening.