Does Neonatal BCG Vaccination Help Prevent Asthma?
Asthma is a widespread condition that can significantly impact quality of life, and despite advances in treatment, it remains a major public health concern. Preventing asthma remains one of the greatest research challenges. An Australian team recently evaluated whether neonatal vaccination with Bacillus Calmette-Guérin (BCG)—a vaccine developed for tuberculosis—could also serve as an immunomodulatory tool in preventing asthma and allergies.
Background and Research Questions
The idea is not new—previous studies have suggested that BCG might exert immunomodulatory effects beyond tuberculosis prevention, potentially influencing the development of allergic and autoimmune diseases.
While studies on animals (particularly mice) have shown promising results, findings in humans have been inconclusive. Moreover, until now, no randomized controlled trial had evaluated this hypothesis in detail. The MIS BAIR study was designed to fill this gap, focusing on asthma, infections, and allergies in children.
Study Design
This multicenter phase III randomized controlled trial took place in Victoria, Australia. A total of 1,272 infants were enrolled between August 2013 and September 2016 and randomly assigned in a 1 : 1 ratio to either receive the BCG vaccine (n = 637, 0.05 mL BCG-Denmark intradermally in the left deltoid region) or no vaccine (n = 635).
The study consisted of two parts: Part 1 (birth to 1 year of age) and Part 2 (1 to 5 years of age), with 80.7% (1,027) of children continuing into Part 2. The primary outcome was asthma prevalence at age 5, assessed via the ISAAC questionnaire and additional questions on asthma medication. Secondary outcomes included active asthma, wheezing illness, asthma severity, and use of preventive medications.
Participant Characteristics
Both groups were well balanced. Roughly half the children were girls (49.5%), with an average birth weight of 3.4 kg and gestational age of 39.3 weeks. Infants were randomized at approximately 47 hours of age. Births were evenly distributed across seasons, with ~64% delivered vaginally.
Mothers had an average age of 32.6 years; 54% were first-time mothers. Smoking during pregnancy was low (3.4%), but 17.5% of households had a smoker during pregnancy. By age 5, 22% of children had been exposed to tobacco smoke; 52.5% of families had a dog, and 37% a cat.
Family history of asthma was reported in 45.5% of parents, and 82.5% reported atopy. About 30% of children had two parents with allergic conditions.
Key Findings
Complete data for the primary outcome were available for 777 children (432 BCG, 345 control). Asthma was reported in 14.4% of children in the BCG group versus 16.0% in the control group (adjusted risk difference [aRD] −1.7 percentage points; 95% CI −7.4 to 3.9). Similar trends were observed for severe asthma and preventive medication use, with aRDs of −3.9 (95% CI −7.7 to 0.0) and −5.6 (95% CI −10.9 to −0.4), respectively, favoring the BCG group.
Children with a family history of asthma had a higher likelihood of developing asthma. Among high-risk children (both parents with asthma), asthma prevalence was lower in the BCG group (17.6% vs. 24.7%), although this difference was not statistically significant (aRD −7.2; 95% CI −15.9 to 1.5).
Post hoc subgroup analyses revealed that children with allergic sensitization had a higher baseline risk of asthma. Among these, BCG vaccination reduced asthma incidence by 6.2 percentage points (17.6% vs. 23.3%), corresponding to a number needed to treat (NNT) of 18. However, interaction tests again did not reach statistical significance.
The effect of vaccination varied by sex, appearing stronger in girls, though this interaction was also not statistically significant.
Conclusion
In the MIS BAIR randomized controlled trial, neonatal BCG vaccination was associated with a slight reduction in asthma incidence, particularly in cases of severe asthma and among high-risk children. However, a clinically meaningful protective effect on asthma incidence was not demonstrated.
Any potential benefits of BCG vaccination must be weighed against known risks, such as disseminated BCG infection in children with rare congenital immunodeficiencies. Further studies with larger, high-risk populations are needed to confirm these findings and explore long-term effects.
Editorial Team, Medscope.pro
Source:
Pittet L. F., Forbes E. K., Donath S. et al.; Melbourne Infant Study: BCG for Allergy and Infection Reduction (MIS BAIR) Group. Neonatal BCG vaccination to prevent asthma: results from the MIS BAIR randomized controlled trial. Pediatr Allergy Immunol 2025 Jun; 36 (6): e70110, doi: 10.1111/pai.70110.
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