Albert 2003.

Methods	Factorial design, individually‐randomized trial conducted in Dhaka, the capital city of Bangladesh
Participants	Eligibility: children aged 2‐5 years of either sex, vitamin A deficiency (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 were included. Children who had received vitamin A supplementation during the preceding 6 months or who had a history of night blindness or sickness due to underlying illnesses such as diarrhoea or respiratory tract infections were excluded. Sample: 256 children
Interventions	4 groups: Group I: vitamin A. Children were given 5 mL (200,000 IU) of vitamin A syrup 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 Group II: zinc. Children received 5 mL of zinc acetate syrup (containing 20 mg of elemental zinc) daily and a single dose of a placebo syrup, according to the same schedule used for the children in the A group Grpup III: vitamin A + zinc. Supplementation with both vitamin A and zinc Group IV: 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: this study seems to be free of other bias