A Cochrane review included 59 papers of 60 studies. The studies included any interventions to prevent viral transmission of respiratory viruses (isolation, quarantine, social distancing, barriers, personal protection and hygiene). Study design included RCTs, cohort studies, case-control studies, cross-over studies, before-after, and time series studies. The highest quality cluster RCTs suggested that respiratory virus spread may be prevented by hygienic measures such as handwashing around children up to 24 months (RR 0.90, 95% CI 0.83 to 0.97), although the decrease was not significant in older children (RR 0.95, 95% CI 0.89 to 1.01). Perhaps this was because younger children are least capable of hygienic behaviour themselves, and have longer-lived infections and greater social contact, thereby acting as portals of infection into the household. Additional benefit from reduced transmission from children to other household members was broadly supported in results of other study designs. Six case-control studies suggested that implementing barriers to transmission, isolation, and hygienic measures are effective at containing respiratory virus epidemics. Limited evidence suggested that the more uncomfortable and expensive N95 masks were superior to simple surgical masks. The incremental effect of adding virucidals or antiseptics to normal handwashing to decrease respiratory disease remained uncertain. Global measures, such as screening at entry ports, were not properly evaluated. There was limited evidence that social distancing was effective especially if related to the risk of exposure.
Comment: The quality of evidence is downgraded by inconsistency (heterogeneity in interventions and outcomes) and by study quality (various study designs with typical sources of bias).