[jlisenbe]

Seems like that is a concept that was mentioned here on a number of occasions.

[tomder55]

Researchers have discovered what was obvious ;natural immunity is the best defense.

Researchers use challenge trials to understand infections and quickly test vaccines and therapies. In March 2021, after months of ethical debate, UK researchers launched the world’s first COVID-19 challenge trial. The study identified a minuscule dose of the SARS-CoV-2 strain that circulated in the early days of the pandemic that could infect about half of the participants, who had not previously been infected with the virus (at that time, vaccines weren’t yet widely available).
In parallel, a team led by Helen McShane, an infectious-disease researcher at Oxford, launched a second SARS-CoV-2 challenge study in people … who had recovered from naturally caught SARS-CoV-2 infections, caused by a range of variants. The trial later enrolled participants who had also been vaccinated.
…When nobody developed a sustained infection, the researchers increased the dose by more and more in subsequent groups of participants, until they reached a level 10,000 times the initial dose. A few volunteers developed short-lived infections, but these quickly vanished.

Scientists tried to give people COVID — and failed (nature.com)