Scientists in the UK have begun testing the BCG vaccine, developed in 1921, to see if it can save lives from Covid.
The vaccine was designed to stop tuberculosis, but there is some evidence it can protect against other infections as well.Around 1,000 people will take part in the trial at the University of Exeter.
But while millions of people in the UK will have had the BCG jab as a child, it is thought they would need to be vaccinated again to benefit.
Vaccines are designed to train the immune system in a highly targeted way that leaves lasting protection against one particular infection.
But this process also causes wide-spread changes in the immune system. This seems to heighten the response to other infections and scientists hope it may even give our bodies an advantage against coronavirus.
--Previous clinical trials have shown the BCG jab reduced deaths by 38% in newborns in Guinea-Bissau, mostly by reducing cases of pneumonia and sepsis.
--Studies in South Africa linked the vaccine to a 73% reduction in infections in the nose, throat and lungs; experiments in the Netherlands showed BCG reduced the amount of yellow fever virus in the body."This could be of major importance globally," Prof John Campbell, of the University of Exeter Medical School, told the BBC.