Vitamin A supplementation at 6-72 months of age has become a mainline intervention for improving survival in populations with endemic vitamin A deficiency.1 However, in the same setting, supplementation at 1-6 months of age has little or no effect on mortality, whether given with immunisation or not.2 3

Giving vitamin A supplements to newborns within the first few days of life significantly reduced early infant mortality in Asian populations with endemic maternal vitamin A deficiency andhigh infant mortality.4 5 6 In Africa, however, this strategy had no beneficial effect on early infant survival in an urban setting7 or—as reported in the accompanying paper by Benn and colleagues—in a peri-urban setting.8

How can these findings be reconciled? Some might suggest that a meta-analysis of all the newborn dosing studies would provide a more accurate estimate of the true effect on early infant mortality. But combining these studies would be a fundamental mistake, because the variation in effect on early infant …