New WHO-funded study reveal possible N95 mask advantages
N95s are more effective for healthcare workers
by KEVIN KUO, DDS, MMSc | June 3, 2020
A new, WHO-funded systemic review and meta-analysis were conducted by a group of researchers from Canada and Lebanon. The study attempted to bring light to several COVID-19 questions regarding transmission prevention in health-care and non-health-care settings.
The review and analysis utilized WHO-specific and COVID-19-specific sources—consisting of 172 studies for the systemic review and 44 studies for the meta-analysis—to obtain transmission data for a few viruses, including SARS-CoV-2, coronaviruses, and MERS. Their findings were as follows:
Our search identified 172 observational studies across 16 countries and six continents, with no randomised controlled trials and 44 relevant comparative studies in health-care and non-health-care settings (n=25 697 patients). Transmission of viruses was lower with physical distancing of 1 m or more, compared with a distance of less than 1 m (n=10 736, pooled adjusted odds ratio [aOR] 0·18, 95% CI 0·09 to 0·38; risk difference [RD] −10·2%, 95% CI −11·5 to −7·5; moderate certainty); protection was increased as distance was lengthened (change in relative risk [RR] 2·02 per m; pinteraction=0·041; moderate certainty). Face mask use could result in a large reduction in risk of infection (n=2647; aOR 0·15, 95% CI 0·07 to 0·34, RD −14·3%, −15·9 to −10·7; low certainty), with stronger associations with N95 or similar respirators compared with disposable surgical masks or similar (eg, reusable 12–16-layer cotton masks; pinteraction=0·090; posterior probability >95%, low certainty). Eye protection also was associated with less infection (n=3713; aOR 0·22, 95% CI 0·12 to 0·39, RD −10·6%, 95% CI −12·5 to −7·7; low certainty). Unadjusted studies and subgroup and sensitivity analyses showed similar findings.
In other words, the authors interpreted the data to conclude that social distancing reduces infection risk in a community setting, with masks and safety glasses playing a beneficiary role. In the healthcare setting, their interpretation suggests that N95 respirators provide much better protection than surgical masks.
Author commentary: Although this study is a systemic review and meta-analysis, the overall level of evidence is still limited. There is not enough evidence to change policies confidently. Different types of viruses were considered. There were no randomized control trials included. The studies included in the systematic review and meta-analysis contain potential bias that may skew results. Nevertheless, the authors did acknowledge these limitations and did their best effort to compile the data available.
