Methods: Randomised double-blind placebo-controlled trial: 3000 children will be randomised to receive either 6 doses of vitamin D or placebo. The first dose will be given at the start of autumn and the second and subsequent doses every 3 months thereafter; children will be followed for 18 months. Incidence of pneumonia will be ascertained though weekly home visits (active surveillance) and from attendances and admissions at the trial clinic and wards in the hospital serving the study area (passive surveillance).