Scientists at Imperial College London have discovered a troubling vulnerability in the human immune system: infection with seasonal flu appears to cripple the body's defenses against tuberculosis, leaving people at risk for a disease that infects roughly 11 million people each year and remains one of the world's leading causes of death from infectious disease.
The discovery came through an unusual research approach. Imperial's human challenge studies program intentionally infected healthy volunteers with influenza under controlled medical conditions, then examined their blood samples before and after infection. Researchers infected those blood samples with TB mycobacterium and measured how well the immune system kept the bacteria in check. The results were stark: participants who developed influenza showed significantly higher mycobacterial growth in their blood compared with their own baseline before infection, and compared with volunteers who never caught flu at all.
The culprit turned out to be a disruption of type 1 interferon signaling—a critical immune pathway that has previously been shown to be essential for containing TB's spread. When flu knocked out this pathway, TB gained a foothold. "This study provides the first direct evidence in humans that influenza infection impairs the body's ability to control the growth of the bacteria responsible for tuberculosis," said Dr. Claire Broderick, clinical lecturer in Imperial's Department of Infectious Disease and first author of the paper published in Nature Communications.
What makes this finding potentially transformative is its practical implication. In regions where TB prevalence runs high—India, Indonesia, and South Africa among them—seasonal flu vaccines could become a powerful new tool for TB prevention. Broderick explained the stakes: "What this means is that a seasonal virus could weaken our ability to fend off TB—which remains a major cause of illness and death around the world."
The timing of this research carries particular urgency. Some TB strains have become increasingly resistant to antibiotics, creating multidrug-resistant tuberculosis (MDR-TB) that is far harder to treat. Flu vaccination offers a potential solution that would be both cost-effective and accessible in regions most burdened by TB.
Yet the work ahead is substantial. Using human challenge studies allowed researchers to tease out complicated interactions and identify immune pathways that cannot easily be observed in patients infected naturally in the real world. The controlled environment revealed mechanisms that open new avenues for prevention. But moving from controlled laboratory conditions to population-wide impact requires what Broderick calls the next critical step: "What we need now is support for large-scale trials to test this and see how effective this approach could be. Given the huge burden from TB, it's crucial we explore new strategies to control the disease."
Those trials could reshape how the world approaches TB prevention. Rather than waiting for tuberculosis to strike, public health programs in high-prevalence regions could prioritize flu vaccination as a means of keeping people's immune systems strong enough to fend off TB on their own. The research suggests that sometimes the most powerful defense against one disease lies in preventing another.