Cherian 2001.

Study characteristics
Methods	Individually randomised trial conducted in India
Participants	Eligibility: children aged 12–60 months with recurrent respiratory tract infections Excluded: children with mild or moderate asthma; who were receiving vitamin supplements or who had received a massive dose of vitamin A in the previous 6 months; with pre‐existing congenital heart disease, chronic lung disease, pulmonary tuberculosis or immunodeficiency disorders; receiving immunosuppressive drugs; with clinically apparent VAD Sample: 61 children; 30 in vitamin A group, 31 in placebo group. Mean age 35.7 months. 60.7% boys
Interventions	Experimental group: single‐dose vitamin A 200,000 IU Control group: placebo in arachis oil Follow‐up: 6 months
Outcomes	Incidence of respiratory disease, mean vitamin A serum levels
Notes	Definition of respiratory illness used was not specific enough.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Eligible children were randomly allocated to receive either 200,000 IU of vitamin A in arachis oil or a placebo containing arachis oil without vitamin A". Comment: details of sequence generation not specified.
Allocation concealment (selection bias)	Unclear risk	Comment: insufficient information to permit judgement.
Blinding (performance bias and detection bias) Blinding of participants	Unclear risk	Quote: "Eligible children were randomly allocated to receive either 200,000 IU of vitamin A in arachis oil or a placebo containing arachis oil without vitamin A".
Blinding (performance bias and detection bias) Blinding of provider	Unclear risk	Comment: not mentioned.
Blinding (performance bias and detection bias) Blinding of outcome assessor	Unclear risk	Comment: not mentioned.
Incomplete outcome data (attrition bias)	Unclear risk	Quote: "Of the 61 included children, seven (3 in the placebo group and four in vitamin A group) did not return for follow‐up" (second page). Comment: authors did not address the reasons for losses to follow‐up, and given the small size of this trial, bias may or may not be introduced depending on why the losses occurred by group. Given this lack of discussion, it is difficult to judge whether there is a low or high risk of bias, but it is likely to be high.
Selective reporting (reporting bias)	Unclear risk	Quote: "Details of doctor or outpatient visits and hospital cough, wheezy breathing, shortness of breath and fever. Details of doctor or outpatient visits and hospital admissions during the study period were also recorded. During each monthly follow‐up visit, the entries in the monthly calendar were reviewed with the parent". Comment: hospitalisation data were not reported though they were collected.
Other bias	Unclear risk	Comment: very little information provided in the paper; difficult to assess.