The team found that babies who took this concoction had a significantly lower risk of developing sepsis—a life-threatening condition where infections trigger body-wide inflammation, restricted blood flow, and organ failure. Sepsis is one of the biggest killers of newborn babies, ending around 600,000 lives every year when they’ve barely begun. Some proportion of these cases begin in the gut, and probiotics might be able to prevent them by ousting harmful microbes, or by stopping benign ones from crossing into the bloodstream and causing infections.

Sure enough, in Panigrahi’s trial, just 5.4 percent of the infants who took the synbiotic developed sepsis in their first two months of life, compared to 9 percent of those who received a placebo. That’s a reduction of 40 percent. Such estimates always come with a margin of error, but the team calculate that the reduction in risk should still be somewhere between 25 and 50 percent.

The effect was twice as large as what the team expected, especially since the infants took daily doses of the synbiotic for just one week. And given the clear evidence of benefits, independent experts who were monitoring the study decided to stop the trial early: It would have been unethical to continue depriving half the newborns of the treatment. Panigrahi originally planned to enroll 8,000 babies into the study. He stopped at 4,557.

Which is still a huge number! Probiotics trials have been criticized in the past for being small and statistically underpowered. Those that looked at sepsis, for example, usually involved just 100 to 200 babies, making it hard to know whether any beneficial effects were the result of random chance. The biggest trial to date included 1,315 infants; Panigrahi’s study is over three times bigger. “[It] exemplifies how intervention research should be done,” writes Daniel Tancredi from the University of California, Davis, in a commentary that accompanies the paper.

“In most studies, people take the probiotics that are available on the shelf without asking why that probiotic should work in the disease they’re interested in. And they think they’ll stumble onto something good,” says Panigrahi. “It’s counter-intuitive, but we did the same thing.”

At first, his team tested Lactobacillus GG and Lactobacillus sporogenes—the most commonly used probiotics in India—in small pilot studies. Both strains are claimed to colonize the gut. “We did the trial and the colonization was almost zero,” says Panigrahi. To find more suitable strains, the team collected stool from healthy volunteers and screened the microbes within for those that could stick to human cells, and could prevent disease-causing bacteria from doing so. They ended up with a strain called Lactobacillus plantarum ATCC strain 202195, which not only colonized infant guts successfully, but stayed there for up to four months. That’s when they launched the big trial.