Finlay and Turvey’s team is continuing to follow the health of the first group of children, studying which go on to develop true asthma—so far, more than a third of those who developed the early signs of the disease have the full-blown version. In addition—since the microbiomes of people in various cultures are known to differ—they’re repeating the experiment in a larger, more diverse set of children, including some from Ecuador, to see whether the four strains of bacteria are universally important.