Nearly one quarter of the world's population undetected carrier of bacteria
Tuberculosis is an infectious disease that is spread through the air; the Mycobacterium tuberculosis that causes it is released in tiny droplets when a tuberculosis patient coughs. Someone else can subsequently inhale the bacteria, which settles in the lungs. As soon as that happens, the person in question is infected.
Tuberculosis continues to take a toll, causing about 1.5 million deaths each year. However, infection does not immediately lead to illness in everyone. Most people carry the bacteria undetected and do not exhibit any symptoms. We call this situation ‘latent tuberculosis infection'. An estimated one quarter of the world's population (about two billion people!) are undetected carriers of the bacteria.
Latent tuberculosis can become active
In the case of a latent tuberculosis infection, our immune system keeps the bacteria in check. As a result, the bacteria do not not multiply and will not spread further. There is a risk that these ‘sleeping’ bacteria will wake up, for example when the immune system is temporarily weakened, due to illness or medication. Sleeping bacteria can thus become active again and still cause illness. By coughing, this type of patient causes the bacteria to spread again. A new vaccine can break this vicious cycle.
Fellow researchers tested a new vaccine (M72:AS01E) for its ability to prevent the development of tuberculosis in latently infected individuals in a major clinical study (involving people) in Kenya, South Africa and Zambia. This was preceded by more than 10 years’ worth of preclinical research that included animal testing; studies with mice, guinea pigs, and macaques were required in order to determine whether the vaccine is safe and effective.
The final results of the clinical study were made public last week. They look promising. Three years after vaccination, only 13 of the 1,626 participants had developed active tuberculosis. In the control group that was not vaccinated, that number was 26 out of 1,663. In other words, the vaccine appears to offer 50% protection against latent tuberculosis becoming active.
More work to be done
If this result is repeated in follow-up studies on a larger scale, then we will make progress in our fight against latent tuberculosis. Whether the vaccine also protects against primary infection is unknown at this point. Meanwhile, product developers and researchers continue to work on improving tuberculosis vaccination.
In any case, the current result offers the hope that we will eventually be able to use vaccination to stop the transmission of tuberculosis.