Barreto 1994.

Study characteristics
Methods	Individually randomised trial conducted in Serrinha, Brazil
Participants	Eligibility: children aged 6–48 months Excluded: presence of xerophthalmia or measles infection within the previous 30 days; children who received a high‐dose VAS in previous 6 months or had weight‐for‐age < 60% of the statistical median Sample: 1240 children; 620 in vitamin A group, 620 in placebo group. Mean age 28 months. 52% boys
Interventions	Experimental group: vitamin A 100,000 IU for children aged < 12 months and 200,000 IU for children aged > 12 months Control group: placebo Study duration: intervention delivered every 4 months for 1 year
Outcomes	All‐cause mortality, incidence and prevalence of diarrhoea and respiratory tract disease, incidence of measles and xerophthalmia
Notes	Study area had inadequate public health services. A previous survey in the area showed a biochemical deficiency (serum vitamin A concentration < 0.35 mmol/L) rate of 7.4% in children of this age group. According to WHO criteria, VAD should be considered a public health problem in this area. The surveillance for morbidity outcome was performed 3 times/week for 1 year, so the recall period was 48–72 hours. We used data for incidence of measles and xerophthalmia from account of attrition in study results section. According to WHO, Brazil does not have a high child mortality rate (i.e. < 40/1000).
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Children were randomly assigned to receive vitamin A or placebo four times‐at the start of the trial and every 4 months thereafter". Comment: authors did not specify the method of sequence generation.
Allocation concealment (selection bias)	Low risk	Quote: "… only an external investigator had the codes for the individually wrapped and numbered capsules". Comment: although specific details were not disclosed, the available information suggested that allocation was adequately concealed.
Blinding (performance bias and detection bias) Blinding of participants	Low risk	Quote: "The gelatinous capsules of vitamin A and placebo (supplied by Hoffman La Roche) were identical in appearance and were unwrapped just before administration". Comment: study was double‐blind, with identical presentation and dosing of vitamin A and placebo.
Blinding (performance bias and detection bias) Blinding of provider	Low risk	Quote: "The gelatinous capsules of vitamin A and placebo (supplied by Hoffman La Roche) were identical in appearance and were unwrapped just before administration". Comment: probably done.
Blinding (performance bias and detection bias) Blinding of outcome assessor	Low risk	Quote: "The study was kept double‐blind and only an external investigator had the codes for the individually wrapped and numbered capsules". Comment: if the assessors were not involved in the allocation process as suggested by the available information, outcome assessors were likely to have been blinded to treatment group assignment.
Incomplete outcome data (attrition bias)	Low risk	Quote: "The total loss in follow‐up time was 10.3%, equally distributed between the study groups". Comment: the rate of attrition was balanced between groups and was primarily attributable to migration. On that basis, attrition bias is not likely to have impacted on the results of the review.
Selective reporting (reporting bias)	Unclear risk	Comment: protocol for the study was not available and, as such, this aspect of the reporting of the study could not be assessed.
Other bias	Low risk	Comment: study appeared free of other potential bias.