BCG Vaccination: A Role for Vitamin D?

Background: BCG vaccination is administered in infancy in most countries with the aim of providing protection against tuberculosis. There is increasing interest in the role of vitamin D in immunity to tuberculosis. This study objective was to determine if there was an association between circulating 25(OH) D concentrations and BCG vaccination status and cytokine responses following BCG vaccination in infants. Methods: Blood samples were collected from UK infants who were vaccinated with BCG at 3 (n = 47) and 12 (n = 37) months post BCG vaccination. These two time-points are denoted as time-point 1 and time-point 2. Two blood samples were also collected from age-matched unvaccinated infants (n = 32 and 28 respectively), as a control group. Plasma vitamin D concentrations (25(OH) D) were measured by radio-immunoassay. The cytokine IFN gamma was measured in supernatants from diluted whole blood stimulated with M. tuberculosis (M.tb) PPD for 6 days. Results: 58% of infants had some level of hypovitaminosis (25(OH) D <30ng/ml) at time-point 1, and this increased to 97% 9 months later. BCG vaccinated infants were almost 6 times (CI: 1.8-18.6) more likely to have sufficient vitamin D concentrations than unvaccinated infants at time-point 1, and the association remained strong after controlling for season of blood collection, ethnic group and sex. Among vaccinees, there was also a strong inverse association between IFN gamma response to M.tb PPD and vitamin D concentration, with infants with higher vitamin D concentrations having lower IFN gamma responses. Conclusions: Vitamin D may play an immuno-regulatory role following BCG vaccination. The increased vitamin D concentrations in BCG vaccinated infants could have important implications: vitamin D may play a role in immunity induced by BCG vaccination and may contribute to non-specific effects observed following BCG vaccination.