Non-medical cloth masks can limit transmission of Covid-19

In the course of the Covid-19 pandemic, recommendations on the effectiveness of masks and the personal protection they provide have changed significantly.

But what about cloth masks for the general public? Canadian researchers have published a study based on an evidence-based, risk-based approach.

All over the world, governmental authorities and institutions are increasingly recommending the use of “non-medical” cloth masks to limit the risk of spreading Covid-19. In a recent publication, researchers from McMaster University and St. Joseph’s Hospital in Ontario explain that there is currently sufficient knowledge to justify this policy.

“Cloth does not stop isolated virions. However, most virus transmission occurs via larger particles in secretions, whether aerosol or droplets, which are generated directly by speaking, eating, coughing, and sneezing … Every virus-laden particle retained in a mask is not available to hang in the air as an aerosol or fall to a surface to be later picked up by touch,” point out the authors of the study.

Supervised by researcher Catherine M. Clase, the study was published on 22 May in the journal Annals of Internal Medicine.

In support of their arguments, the authors of the publication cited several previous studies of cloth masks, notably a randomised controlled trial conducted in 2015 and published in BMJ Open, which aimed to compare cloth masks with medical masks.

According to the study, the rate of infections with influenza-like illnesses among health professionals wearing cloth masks was 2.3%, compared to 0.7% for medical masks. However, the results of this study were the subject of a second publication in the light of recent events linked to the Covid-19 pandemic.

“This trial has been misinterpreted as showing that cloth masks increase risk for influenza-like illness, but it actually provides no evidence on the effectiveness or harms of wearing cloth masks compared with not wearing cloth masks because it had no comparator group without masks. Furthermore, filtration efficiency for the cloth masks used in this study was 3%,” notes Clase’s team.

The Canadian researchers therefore draw attention to the effectiveness of cloth masks, not with regard to surgical or FFP masks, but rather in comparison to no masks at all.

Before concluding: “No direct evidence indicates that public mask wearing protects either the wearer or others. Given the severity of this pandemic and the difficulty of control, we suggest that the possible benefit of a modest reduction in transmission likely outweighs the possibility of harm.”

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