Page "Bacillus Calmette–Guérin" Paragraph 18

# Exposure to ultraviolet light: Concentration of ultraviolet light ( particularly UVB light ) from the Sun may have some effect on efficacy of the BCG vaccine.

UVB has been demonstrated to reduce efficacy of BCG vaccine in laboratory guinea pigs.

The concentration gradient of UVB light increases geographically closer to the Earth's equator.

Though currently unresearched, this effect possibly occurs as a result of sunlight-dependent vitamin D production.