Divulgação, Notícias

Tuberculosis: BCG prevents disease in young children but not in adults

Researchers investigated the impact of BCG in children on development and mortality from pulmonary and extrapulmonary tuberculosis


At the age of 101 BCG is the only vaccine ever given to treat tuberculosis, a disease that affects more than 10 million people a year

A study published in The Lancet found that the bacillus Calmette-Guérin (BCG) vaccine applied in the newborn for prevention against tuberculosis (TB), provides significant protection only in children under 5 years of age. According to the article, BCG did not provide protection among participating adolescents or adults. The results of the article entitled Infant BCG vaccination and risk of pulmonary and extrapulmonary tuberculosis throughout the life course: a systematic review and individual participant data meta-analysis, argues that children over 10 years and adults could benefit from a booster dose, especially if a new vaccine is developed that guarantees protection after childhood. Another important finding, among the four studies with mortality data, was the protection of 75% of BCG against death (0.25, 95% CI 0.13 – 0.49).

For the systemic review, 26 longitudinal studies were selected, conducted in 17 countries, which included almost 70 thousand participants exposed to tuberculosis between 1998 and 2018. Of these, 1,782 (2.6%) developed tuberculosis, being 1,309 (2.6%) among the 49,686 vaccinated with BCG and 473 (2.5%) among the 18,866 unvaccinated. The overall effectiveness of BCG against all types of tuberculosis was 18% (0.82, 95% CI 0.74 – 0.91). Evaluating the 14 cohort studies with information on tuberculosis type (pulmonary or extrapulmonary), BCG offered significant protection against pulmonary tuberculosis among all participants (0.81, 95% CI 0.7 – 0.94), but not against extrapulmonary tuberculosis. By focusing only on pulmonary TB, BCG was 19% effective, but this effect also occurred only among young children.

Stratified by age, the study showed that BCG significantly protected only children under five years of age against all types of tuberculosis (0.63; 95% CI 0.49 – 0.81). When evaluating only the contacts with a positive tuberculin test, protection occurred in participants of all ages (0.81; 95% CI 0.69 – 0.96), including those younger than 5 years 95% CI 0.47 – 0.97) and between 5 and 9 years 95% CI 0.38 – 0.99). There was no protective effect among those with negative tests, except in children under 5 years of age. Also according to the results of the study, BCG was 37% effective among all children under 5 years of age. No conclusive evidence was found that the vaccine protects children over 10 years of age or adults.

According to the president of the Brazilian Society of Tropical Medicine (SBMT), Dr. Julio Croda, one of the authors of the study, the findings provide updated evaluations on the efficacy of BCG, since most previously published studies on the subject were conducted more than 50 years ago, with varied results and especially in environments with a relatively low burden of the disease. This systematic review, with meta-analysis of the individual data of the participants, of studies available in the MEDLINE, Web of Science, BIOSIS, and Embase databases, without language restrictions, presents data from the last 20 years, from high-load environments in 17 countries, including Brazil, South Africa, China, Vietnam, Indonesia, Uganda and The Gambia.

The analysis examined the variability between studies, including the use of skin and blood TB infection tests, and took into account potentially confounding factors such as HIV, exposure status, and previous history of TB, among others. “The primary outcome was the diagnosis of tuberculosis in contacts exposed to the disease and the secondary outcomes were the diagnosis of pulmonary and extrapulmonary tuberculosis and mortality. After adjusting for variables, the results were stratified by age and Mycobacterium tuberculosis infection status,” explains Dr. Croda.

Finally, the president of SBMT recalls that the vast majority of cases of tuberculosis in the United States and other high-income countries occur in immigrants from places with a high burden of the disease, usually low-income countries. “Although our results are mainly in environments with a high burden of tuberculosis, they are also relevant to low burden locations, that is, our findings bring important implications for rich and poor countries,” he emphasizes by highlighting the importance of substantial investments in the development of vaccines against tuberculosis so that the disease can be controlled globally. “Countries should also consider reinforcements in immunization against tuberculosis after childhood and, for this, we urgently need effective vaccines for adults. There are several candidates under study and we hope that one or more will prove to be effective”, he concludes.