The Economist.
Around 15 years ago, Mihai Nitea, an immunologist at the Radboud University Medical Centre in the Dutch city of Nijmegen,
was investigating how a particular vaccine works.
We were studying the BCG vaccine and what are the immune mechanisms which are induced by BCG vaccine
to help us defend against tuberculosis.
The BCG vaccine was designed more than a century ago.
It's still used today to protect people from tuberculosis or TB.
In their lab, Mihaly and his team exposed vaccinated people's cells to the bacteria which causes TB.
At the same time, we also have used another microorganism as a control, a fungus called candida, because we knew, well,
in principle, BCG should not change the responses to other type of bacteria or viruses or fungi.
But something rather surprising happened in that control group.
We could observe protection also against candida.
And then we tested a number of other microorganisms and we observed that indeed the protection was much broader.
And at that time point, we could not understand what is happening because this was against,
well, all the immunology books.
The astonished researchers wanted to understand why they'd seen the BCG vaccine work on so many different pathogens.
Bugs that the vaccine had not been designed to protect against.
So they looked at historical data.
Actually, when BCG started to be used in the population 100 years ago,
the mortality due to various types of infections decreased dramatically by more than 50%.