This will be done in two studies of newborn children. Study A includes 6,000 normal birth weight infants (> 2500 g) randomized to 50,000 or 25,000 IU vitamin A or placebo given simultaneously with BCG vaccine. Study B includes 1,600 low birth weight infants (< 2500 g) randomized to vitamin A or placebo and early BCG or late BCG in a two-by-two factorial design. The studies take place in Guinea-Bissau, West Africa. The study area consists of five districts in the capital of Guinea-Bissau. The Bandim Health Project has been working in the study area for almost 25 years, and a demographic surveillance system has been established and has functioned for many years.