Volunteers have been exposed to the Covid-19 coronavirus as part of a clinical study.
koto_feja/GETTY
Deliberately exposing other people to the coronavirus that causes covid-19 as part of a so-called risk study helped us understand why some people seem immune to infection.
In the first study of its kind on covid-19, conducted in 2021, a group of foreign researchers evaluated 16 other people with no known health conditions who had not tested positive for the SARS-CoV-2 virus or been vaccinated against it.
Learn more
How to know if your immune formula is strong or strong
He. . .