Barreto 1994.

Methods	Individually‐randomised trial conducted in Serrinha, Brazil
Participants	Eligibility: children aged 6‐48 months were eligible for inclusion in the trial. The exclusion criteria was presence of xerophthalmia or measles infection within the previous 30 days. Children who received a high dose of vitamin A supplementation in the previous 6 months or had weight‐for‐age less than 60% of the statistical median were also excluded. Sample: a total of 1240 children were included, 620 in vitamin A group and 620 in placebo. Mean age of participants was 28 months, and proportion of boys was 52%
Interventions	The experimental group received vitamin A in a dose of 100,000 IU for children younger than 12 months and 200,000 IU for children older than 12 months. The control group received placebo only. The intervention was 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	The study area had inadequate pubic 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, vitamin A deficiency should be considered a pubic health problem in this area. The surveillance for morbidity outcome was done 3 times/week for 1 year, so the recall period was 48‐72 hours. We took data for incidence of measles and xerophthalmia from account of attrition in 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 do 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 suggests 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: the 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 the 2 treatment 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: the 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: this study appears to be free of other potential bias.