BCG is protective against death in male but not female patients with pulmonary tuberculosis in Guinea-Bissau

With an epidemic traceable to 9,000 years ago and an estimated death toll of one billion in the last two hundred years alone, tuberculosis (TB) has caused immeasurable suffering. Even today, apart from the current COVID-19 pandemic, no infectious disease is a bigger threat to global health than tuberculosis. Indeed, an estimated one quarter of the World’s population is infected with Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis, and in 2021 1.6 million people lost their lives to active TB. Given this fact, there is an urgent need to develop effective strategies to combat the TB epidemic.

Even so, despite recent developments, only one vaccine targeting Mtb is currently on the market – the Bacille Calmette-Guérin (BCG). While this vaccine has been in use since the 1920s, its efficacy is still debated. However, it may be that BCG not only protects against developing TB but modulates the course of the disease. Additionally, research from our colleagues in Bissau and elsewhere have shown it to have beneficial effects beyond protection against TB (non-specific effects).

At the Bandim Health Project in Guinea-Bissau, we have been following a cohort of patients with TB within a defined study area in the capital Bissau since 2004. We also follow the background population within this area with regular censuses. This provides a unique setup for clinical and epidemiological research on tuberculous disease in a low-income setting with a high burden of TB.

One characteristic of TB is the sex disparity in its epidemiology. Globally, almost twice as many males as females develop active TB. In a recent study, published in the TRSTMH, we argued that at least in our setting this was more likely to be due to biological factors than notification bias. In our most recent study, published this month also in the TRSTMH, we wanted to investigate if vaccination with BCG modulates the course of disease in our cohort of patients with TB. Using mortality statistics, we compared patients who had the characteristic BCG scar with those who did not. Moreover, as recent studies have shown that the beneficial non-specific effects of BCG correlate positively with scar size, we decided to compare groups further by scar size. Finally, we wanted to see if there were differences between the sexes in any effect we might find.