C
Size: a a a
C
N
SR
U0
U0
🤖F
There is limited evidence on the effectiveness of medical face masks for the prevention
of COVID-19 in the community. We identified only one randomised controlled trial (RCT), with around 3 000
participants in each of the intervention (medical face mask) and the control group [19]. The study showed an
18% decrease in the incidence of COVID-19 among people in the intervention group compared to the control
group; however, this difference was not statistically significant. Although this study was conducted at a time of
low incidence of COVID-19, leading to a relatively low number of events, the results support a relative reduction
of risk lower than 50%. There was a risk of bias due to suboptimal compliance with the use of masks in the
intervention group. No conclusion can be drawn from this study on the effectiveness of medical face mask use as
source control (transmission to others), as the study was not designed to assess this. The evidence from this
study is compatible with low or no effect of medical face masks for personal protection in the community, and
the certainty of the evidence is moderate due to risk of bias.
Our search further identified one case-control [20] and four cross-sectional studies [21-24] that assessed the
effectiveness of face masks for the prevention of COVID-19 in the community. These studies did not distinguish
between medical face masks, non-medical face masks and respirators. With only one exception, these studies
showed a very favourable statistically significant effect of face masks (OR range 0.16-0.3). The remaining study -
a cross-sectional study -also showed a favourable effect, but it was not statistically significant. Despite the
consistent favourable effect of face masks for the prevention of COVID-19, the certainty of evidence was
considered low due to serious risk of bias and indirectness in some studies (one study was performed on a U.S.
Navy ship and another in a school)
🤖F
N
D
U0
N
N
U0
N
U0
U0
N
U0
N