When babies in the African countries of Guinea Bissau and Uganda were given the tuberculosis vaccine, something remarkable happened.

Instead of the vaccine only protecting against the target bacteria – Myocbacterium tuberculosis – the tuberculosis vaccine offered broad protection against a range of unrelated infections, including respiratory infections and serious complications such as sepsis.

Australian researchers have now pinpointed the biological mechanism behind the off-target effects of the tuberculosis vaccine.

The team administered the Bacille Calmette-Guérin (BCG) vaccine to 63 infants within ten days of their birth and compared their progress to a control group of 67 infants who did not receive the BCG vaccine.

The researchers took blood samples from the infants and examined circulating white blood cells called monocytes in both groups.

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