Bahl 1999.

Study characteristics
Methods	Individually randomised study conducted in an urban slum of Delhi, India
Participants	Eligibility: infants aged 6–9 months enrolled into study when they turned 9 months old Excluded: infants with history of measles, contact with a case of measles or measles immunisation, or had received a dose of vitamin A in the previous 4 months; serious illness requiring hospitalisation or having clinical signs of VAD (i.e. xerophthalmia, Bitot's spots, etc.) Sample: 618 infants; 309 in vitamin A group, 309 in control group. 50% boys
Interventions	Experimental group: single‐dose vitamin A 30 mg (100,000 IU) in the form of retinol palmitate Control group: soybean oil Follow‐up: 4 months
Outcomes	Antibody response to measles vaccine, incidence of measles during study period, and side effects (e.g. vomiting, drowsiness, etc.) in first 48 hours
Notes	The primary objective of the study was to determine the response to measles vaccine when administered along with vitamin A at 9 months of age. The study found no significant difference in antibody titres between groups 3 months after the administration of intervention. The baseline prevalence of clinical VAD in children aged 1–5 years in the study area was 3.5% and that of biochemical VAD was 37%.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Infants were randomly assigned to receive vitamin A or a placebo by using a simple randomisation scheme with random permuted blocks of size eight, i.e. four infants each out of every eight infants enrolled were randomised to receive vitamin A or a placebo". Comment: probably done.
Allocation concealment (selection bias)	Unclear risk	Comment: insufficient information to permit judgement.
Blinding (performance bias and detection bias) Blinding of participants	Low risk	Quote: "This scheme ensured that all infants received 30 mg vitamin A by 12 mo [months] of age without interfering with the double‐blind design of the study". Comment: probably done.
Blinding (performance bias and detection bias) Blinding of provider	Low risk	Comment: adequate masking of vitamin A and placebo should have meant that providers were adequately blinded.
Blinding (performance bias and detection bias) Blinding of outcome assessor	Low risk	Comment: adequate masking of vitamin A and placebo should have meant that outcome assessors were adequately blinded.
Incomplete outcome data (attrition bias)	High risk	Comment: losses to follow‐up and exclusions described. Missing data excluded from the analysis. It is not possible to ascertain whether the exclusion of data from 17% of participants (equally distributed between treatment groups) would have impacted on the results. The investigators stated that the reason for their exclusion was that a follow‐up serum sample could not be ascertained.
Selective reporting (reporting bias)	High risk	Comment: data on harms are incompletely disclosed in the study report.
Other bias	Low risk	Comment: study appeared free of other bias.