Cochrane review: effectiveness of masks and hand washing
In this systematic review of influenza virus studies, it is concluded that masks do not show efficacy in reducing the spread of influenza-like illness (ILI), but that hand washing can reduce the number of people contracting respiratory viruses.
This report was based on 67 relevant studies conducted in low-, middle- and high-income countries around the world in hospitals, schools, nursing homes, offices, childcare centres and communities during non-epidemic influenza periods, during the global H1N1 influenza pandemic in 2009, and epidemic influenza seasons until 2016.
These are the results:
Hand hygiene can reduce the number of people who catch a respiratory, flu-like illness. The analysis of the 16 studies evaluated (61,372 people) concludes that “hand hygiene is likely to modestly reduce the burden of respiratory disease“, a more effective result than the use of masks.
“In a comparison of hand hygiene interventions with control (no intervention), there was a 16% relative reduction in the number of people with Acute Respiratory Infection (ARI) in the hand-hygiene group (44,129 participants), suggesting a likely benefit.“
Overall, the analysis of the 16 studies (61,372 participants) shows that “hand hygiene may offer a benefit with an 11% relative reduction in respiratory diseases, but with high heterogeneity.“
The report also underlines that there is uncertainty about the effects of face masks.
“The unmoderate certainty of the evidence means that our confidence in the estimate of effect is limited, and that the true effect may differ from the observed estimate of effect. Pooled results from randomised trials did not demonstrate a clear reduction in respiratory viral infection with the use of medical/surgical masks during seasonal influenza. There were no clear differences between the use of medical/surgical masks compared with N95/P2 respirators in healthcare workers when used in routine care to reduce respiratory viral infection.”
- Surgical masks – There were seven studies in the community and two studies with healthcare professionals. Compared to not wearing a mask, wearing this equipment may have made little or no difference to the number of people who got an influenza-like illness (9 studies; 3507 people); and probably no difference to the number of people with laboratory-confirmed influenza (6 studies; 3005 people).
- N95/P2 respirators – Four studies were done with healthcare workers, and one small study was done in the community. Compared to wearing medical or surgical masks, wearing N95/P2 respirators has little or no impact on the number of people confirmed to have flu (5 studies; 8407 people), the number of people getting a flu-like illness (5 studies; 8407 people) or respiratory illness (3 studies; 7799 people).
The authors highlight the high risk of some types of biases that “make it difficult to draw firm conclusions and to generalise the results to the current pandemic of COVID-19.”
“The pooled results of randomised trials showed no clear reduction in respiratory viral infection with the use of medical/surgical masks during seasonal influenza. There were no clear differences between the use of medical / surgical masks compared with N95 / P2 respirators in healthcare workers when used in routine care to reduce respiratory viral infection.“
“Hand hygiene is likely to modestly reduce the burden of respiratory disease.“
“There is a need for large, well-planned RCTs that address the effectiveness of many of these interventions across multiple sites and populations, especially in those at higher risk of ARI (Acute Respiratory Infections).”
Background of the systematic review
Cochrane is an organisation with a matrix of great political and economic independence.
It aims to organise medical research findings to facilitate evidence-based choices about health interventions involving health professionals, patients and policy makers.
The group conducts systematic reviews of health interventions and diagnostic tests, which it publishes in the Cochrane Library.