Does timing of the Bacillus Calmette-Guérin vaccine affect weight in children under the age of 5 years? An observational study in Guinea-Bissau

Introduction: The live Bacillus Calmette-Guérin (BCG) vaccine has beneficial non-specific effects (NSEs) affecting susceptibility to other infections than tuberculosis. The non-live Pentavalent vaccine (Penta) may have negative NSEs on overall health, particularly for girls. We tested whether timing of BCG (scheduled at birth) and first Penta (Penta1) vaccination (scheduled from 6 weeks) were associated with weight-for-age z-score (WAZ) in children under 5 years of age. Methods: Bandim Health Project (BHP) monitors vaccination status of children under 5 years through a Health and Demographic Surveillance System in Guinea-Bissau. Between 2016 and 2020, BHP weighed children eligible for enrolment in two large cluster-randomized trials. We classified BCG as timely if given during the neonatal period and Penta1 as timely if given within 2 months of age. Using linear regression models, we quantified the association between WAZ and timing of vaccination, adjusted for background factors associated with vaccination timeliness. Results: A total of 25,693 children were included in the BCG cohort and 24,400 in the Penta cohort: 46 % had received no neonatal BCG and 54 % no timely Penta1. Children with no neonatal BCG had lower WAZ (adjusted difference − 0.08 (95 % confidence interval (95 %CI) -0.12 to −0.04)). The adjusted difference in WAZ for each week of delay in BCG vaccination was −0.005 (95 %CI -0.007 to −0.003). Associations were similar for boys and girls. Overall estimates for no timely Penta1 were similar (adjusted difference − 0.08 (95 % CI -0.11 to −0.05)) but the difference tended to be larger in males (adjusted difference − 0.10 (95 %CI -0.14 to −0.06)) than in females (adjusted difference − 0.06 (95 %CI -0.11 to −0.02) (p = 0.27 for interaction with sex). Conclusion: Receiving no timely BCG or Penta1 (or none at all) was associated with lower WAZ though much of the difference is likely explained by confounding. Timely Penta1 vaccination seemed less beneficial for girls.