In most TB endemic regions of the world, BCG is given to infants shortly after birth. The vaccination prevents childhood versions of TB and saves thousands of children’s lives annually.
However, the efficacy of BCG wanes over time. In other words, it stops working. Protection against TB is often lost by adolescence or early adulthood.
Importantly, BCG doesn’t prevent active lung TB in adults, the most important driver of ongoing transmission and cause of death.
The World Health Organization has a goal of TB elimination. To do that, we need to find a TB vaccine that also works in adults.
The reasons BCG hasn’t been replaced with a more effective TB vaccine include:
- the decline of TB in many Western countries in the 20th century
- limited interest from pharmaceutical companies to invest in TB vaccine development
- the fact TB research and pre-clinical vaccine development is logistically challenging and requires special biological containment facilities
- the short-term and fiercely competitive environment for government and philanthropic research funding makes it difficult for academics to commit to TB vaccine research as a career path.