The immunological basis for immunization series: module 5: tuberculosis, update 2021

Overview

It is estimated that about one quarter of the global population, approximately 1.7 billion people (2014 estimates), are infected with Mycobacterium tuberculosis and between 5–15% of infected people are expected to progress to tuberculosis (TB) disease during their lifetimes. The risk of progressing from infection to TB disease is highest in the very young, HIV- infected people, smokers, people taking immunosuppressive medication and those with diabetes mellitus. The risk of progression from primary infection to TB disease in the absence of preventive therapy is approximately 30−50% in infancy and 10% in the second year of life, but declines to 2−5% between 5 and 10 years of age, increasing thereafter to 10−20% in adolescents and adults. More than half of the lifetime TB risk is thought to occur in the first two years after infection.

While young children bear the highest risk of progression to disease and the highest risk of severe morbidity in the form of miliary and meningitis disease, the ongoing global TB epidemic is driven by transmission via droplet spread from infectious adolescents and adults with pulmonary TB disease. Therefore, although children bear a disproportionate burden of disease, systematic TB control efforts are directed at halting adolescent and adult disease.