Albert 2003.

Study characteristics
Methods	Factorial design, individually randomised trial conducted in Dhaka, Bangladesh
Participants	Eligibility: children aged 2–5 years of either sex, VAD (serum retinol level < 20 mg/dL; and nutritional status corresponding to a weight‐for‐age score that was 61% of the median National Center for Health Standards standard Excluded: children who had received VAS during the preceding 6 months or with history of night blindness or sickness due to underlying illnesses such as diarrhoea or respiratory tract infections Sample: 256 children
Interventions	4 intervention groups Experimental group I: vitamin A. 5 mL vitamin A syrup 200,000 IU once a week before administration of the first dose of the vaccine and received 5 mL of a placebo syrup every day for 42 days starting 3 weeks before administration of the first dose of vaccine and ending 1 week after the second dose of vaccine Experimental group II: zinc. 5 mL zinc acetate syrup (containing 20 mg of elemental zinc) daily + single dose of a placebo syrup, according to the same schedule used for the children in the A group Experimental group III: vitamin A + zinc Control group: placebo
Outcomes	Vibriocidal antibody response to cholera vaccine
Notes	No clinical outcomes were available so no data were included in meta‐analysis.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "Bottles of syrup were serially numbered according to the randomizations list". Comment: most likely done.
Allocation concealment (selection bias)	Low risk	Quote: "The randomizations code was broken after completion of the study".
Blinding (performance bias and detection bias) Blinding of participants	Low risk	Quote: "The zinc syrup and its placebo syrup looked very similar, as did the vitamin A syrup and its placebo syrup".
Blinding (performance bias and detection bias) Blinding of provider	Low risk	Quote: "The randomization code was broken after completion of the study".
Blinding (performance bias and detection bias) Blinding of outcome assessor	Low risk	Quote: "The randomization code was broken after completion of the study".
Incomplete outcome data (attrition bias)	Low risk	Comment: minimal attrition.
Selective reporting (reporting bias)	Unclear risk	Comment: no trial registration number was available.
Other bias	Low risk	Comment: study appeared free of other bias.