Non-specific Effects of Vaccines and Stunting: Timing May Be Essential

• BCG was associated with lower odds on stunting when given early in life and with higher odds when given later in infancy.
• Similar associations were found for DTP1 and measles vaccination and with hemoglobin concentration as outcome.
• Time-dependency of non-specific effects provides a new perspective in the field although confirmation is required.Vaccines possess effects on health beyond their target disease, so called “non-specific effects”. Our results suggest that timing of vaccination may be important for these effects. In African children, BCG vaccination was associated with lower odds on stunting when given in the first month of life and higher odds on stunting when given later in infancy. Comparable time patterns were found for DTP1 and measles vaccination and with hemoglobin concentration as outcome. Findings were made possible by a Big Data design, using data on 368,450 African children that varied considerably in vaccination times and background characteristics. These results, if confirmed in further research, may provide a fundamental new perspective on the non-specific effects of vaccines.

BackgroundBacillus Calmette-Guérin (BCG) vaccination possesses effects on health beyond its target disease, the so called “non-specific effects”. We evaluate these effects, as well as the effect of timing of BCG and other vaccinations, on stunting in Sub-Saharan African (SSA) children under five.MethodsWe use a Big Data design, including cross-sectional data for 368,450 children from 33 SSA countries. Logistic regression analysis is used with control factors at child, mother, household and context level.ResultsOverall, BCG vaccination did not affect stunting in SSA children (OR 1.00 [0.98–1.03]). Timing of BCG vaccination was of importance (βtime = 0.067 [0.061–0.073]): compared to unvaccinated children, BCG was associated with lower odds on stunting for children vaccinated early in life (OR 0.92 [0.89–0.94]) and higher odds for children vaccinated later in infancy (OR 1.64 [1.53–1.76]). Similar findings were done for diphtheria-tetanus-pertussis (DTP)1 and measles vaccination, and when hemoglobin concentration was used as outcome variable.ConclusionsWe found a general time-dependent pattern of non-specific effects of vaccination, with positive associations for vaccinations given early in life and negative associations for vaccinations given later in infancy. If confirmed in further research, our findings may provide a new perspective on the non-specific effects of vaccination.