High-dose vitamin A to children above 6 months of age reduces all-cause mortality by 23-30%. The WHO recommends vitamin A supplementation (VAS) with the first vaccine after 6 months of age. However, the effect of providing VAS with vaccines has never been investigated. We have hypothesised that the effect of VAS depends on the immune stimulus at the time of supplementation. Hence, the effect might vary depending on which type of vaccine it is given with. In particular, we hypothesised that VAS might be beneficial when given with measles vaccine but not when given with DTP vaccine. Normally the first vaccine after 6 months of age would be a measles vaccine, but many children come late for their DTP vaccinations and receive DTP alone or together with measles vaccine. Hence, it is important to study whether the effect of VAS is the same irrespective of the vaccine(s) administered at the same time.

Guinea-Bissau has not yet implemented the WHO vitamin A policy of providing VAS with vaccines, but plans to do so within the next years. Together with the Ministry of Health in Guinea-Bissau, the Bandim Health Project (BHP) in Guinea-Bissau will investigate the effect on mortality and morbidity of implementing the WHO vitamin A policy in Guinea-Bissau. This will be done in a large randomised trial.

BHP has a demographic surveillance system (DSS) which has followed a population of now more than 150,000 individuals for almost 30 years. Children will be randomised to receive VAS or placebo with their first vaccine after 6 months of age, and will be followed through the DSS to assess mortality and morbidity. Based on previous observations, the effects of VAS might differ according to sex and season. The interaction between VAS, sex, and season will also be studied in the present trial. By identifying situations where VAS may be beneficial, ineffective, or even harmful the study may contribute importantly to optimising the VAS policy for low-income countries.