BCG vaccination and reduced risk of asthma

possibility that BCG vaccination contributes to the prevention of asthma. There have been numerous objections to the methods and results of the study. However, due to the current global epidemic of asthma and the hygiene hypothesis to explain the increase in allergic diseases, (2) as well as to the immediate availability of this safe, low-cost intervention, the expectations surrounding this issue have greatly increased. In its simplest form, the hygiene hypothesis suggests that early exposure to microbial products modulates the immune system away from the mechanisms related to the development of atopy. The infection generated by the attenuated mycobacterium of the BCG vaccine might perform this function, especially if the vaccine is administered in the first months of life. Various studies in humans (in which different methods were used and different populations were investigated) have examined the issue and have obtained negative results or results of limited impact, frustrating the general expectation, which had increased due to evidence from experimental studies. (3) In this issue of the Brazilian Journal of Pulmonology, Sarinho et al. (4) make an important original contribution to the national debate by reporting their observations regarding the effect of the BCG vaccine, the number of doses of which varied, on 2,311 individuals between 10 and 70 years of age. The authors conducted a 10-year retrospective cohort study in which they evaluated those individuals in terms of the incidence of asthma (according to the number of BCG vaccine doses received). No statistically significant differences were found between the groups of individuals who received one, two or three or more doses of the BCG vaccine with regard to the prevalence of asthma, which was 16.4% (216/1,317), 16.6% (107/644) and 14.3% (50/350), respectively. Despite the methodological limitations of a