Twenty trials were included in the review; the overall number of participants was not stated. One of the nine prevention trials was classed as having a low risk of bias, whilst six were at high risk of bias. Seven of nine treatment trials had a low risk of bias. Follow-up in the prevention trials ranged from 90 days to 15 months (where reported).
Pneumonia prevention: When vitamin A was compared with placebo for prevention, there were no significant differences in numbers of children with pneumonia (four trials), incidence of pneumonia (five trials), pneumonia mortality (two trials) and all-cause mortality (four trials). The only outcome that showed evidence of heterogeneity was all-cause mortality (I2=65.6%).
Pneumonia treatment: When vitamin A was compared with placebo for treatment of pneumonia, there were no significant differences in mortality (eight trials), duration of hospitalisation (two trials), duration of illness (two trials), complications (four trials), side effects (two trials), absence of cure (one trial) and hospitalisation of outpatients (one trial). The only outcome that showed evidence of heterogeneity was occurrence of side effects (I2=61.1%).