Australian scientists have revealed the answer to a decades-old mystery – why does the tuberculosis (TB) vaccine, Bacillus Calmette-Guérin (BCG) protect infants from a range of other diseases as well as TB Scientists from Perth’s Telethon Kids Institute have revealed that the BCG jab boosts the immune systems of newborn mice by creating a dramatic and rapid increase in neutrophils – a type of immune cell.
“It’s been known for a very long time that neutrophils play a very important role in managing sepsis, but until now, nobody understood the role of BCG in initiating this critical process,” says Dr Kelly Amenyogbe.
“It was actually thought to be biologically implausible. However, we’ve not only shown how BCG is involved, but that it kicks off this process almost instantly following vaccination – far more quickly than anticipated.”
While “not shocking”, the mechanism wasn’t considered plausible
The team gave the BCG vaccine to newborn mice, which ramped up their production of neutrophils as a result. When they exposed the newborn mice to sepsis three days later, the neutrophils rapidly cleared the infection, and the mice recovered quickly.
“It was a very simple mechanism in the end…In retrospect, it’s really not shocking, yet it was not previously considered plausible,” says Amenyogbe.
To confirm that the reaction seen in the mice also occurs in humans, the team analysed blood samples from 85 newborn babies in Gambia, Guinea-Bissau, and Papua New Guinea, half of whom had been vaccinated.
Three days after vaccination, the newborns who had been given BCG had about twice as many neutrophils in their blood as babies who were unvaccinated.
However, the immune boost provided by BCG in the mice was short-lived, the scientists said, lasting about a fortnight, and it wasn’t seen in adult mice when they were given the vaccine, just in newborn pups.
That highlights the importance of making sure babies get the jab at the most appropriate time, says Professor Tobias Kollmann.
“Around half of all newborn deaths from infection happen in the first week of life…Less than half the babies who should get this vaccine right after birth actually get it then.”
BCG is being trialled in healthcare workers to protect against COVID-19
BCG’s immune-boosting properties mean it is currently being trialled against COVID-19 in healthcare workers in Melbourne, in the hope it will protect them against the virus. Amenyogbe and Kollmann are collaborating in that trial.
“Whether this effect on neutrophils is relevant in terms of coronavirus is hard to say,” says Amenyogbe.
“We know this effect is short lived and…age-dependent. However, there are a lot of known effects of the BCG vaccine on the immune system that are completely independent of neutrophils, and these other effects could be relevant for the coronavirus. Hopefully, we’ll have that answer not too long from now.”
This article was first published on Australia’s Science Channel, the original news platform of The Royal Institution of Australia.