< Masks

Is it useful to collectively wear masks to fight against COVID-19 ?

Text updated on 2020-07-07


When a large proportion of the population wears a face covering, no matter whether it is a medical mask or a homemade cloth mask, it significatively helps fight the COVID-19 by reducing its transmission.

There is no scientific study that has yet measured with certainty the real impact of wearing a mask on the spread of COVID-19. However, it is possible to estimate this impact by using epidemiological models that take into account the effectiveness of masks (their ability to filter out droplets carrying the virus and prevent its transmission between people) and the proportion of people wearing masks. These models indicate that the use of masks can lead to a significant decrease in the "average reproduction rate" (Re or Rt) of the SARS-CoV-2 coronavirus. This is the number of people infected by a single carrier at any given point in the epidemic. If it is less than 1, the epidemic regresses.

If it is greater than 1, the larger the number, the faster the epidemic progresses. In order for the use of masks to have a significant impact on the epidemic, they must be adopted by a sufficient proportion of people, regardless of their symptoms. For example, assuming that a mask prevents 50% of infections, at least 96% of the population would need to wear a mask for Re to be less than or equal to 1, which would stop the epidemic from progressing. And a recent meta-analysis found that masks prevent at least 50% of infections. If the proportion of people wearing masks is lower (e.g., 50 or 70%), wearing a mask alone is not sufficient to stop the epidemic, but it is an effective complement to other control measures, such as containment or tracing of contact cases.

The benefits of collective adoption of masks exist regardless of the severity of the epidemic in the country and other control strategies in place.

Please remember, wearing a mask does not mean you can neglect hand hygiene and social distancing!


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Sources

A review comparing different types of masks (handicraft, surgical...) to fight against COVID-19.

Salvi, S. S. In this pandemic and panic of COVID-19 what should doctors know about masks and respirators?

A review of the literature summarizing the arguments in favour of the use of masks to combat the COVID-19 epidemic. The authors advocate the pervasive use of masks.

Howard, J., Huang, A., Li, Z., Tufekci, Z., Zdimal, V., van der Westhuizen, H. M., ... & Tang, V. (2020). Face masks againstCOVID-19: an evidence review.

Two mathematical models show the effect of masks on the effective reproduction rate (Re) of SARS-CoV-2, and on pandemic control. These models take into account the proportion of people adopting the mask, the conditions of adoption, the effectiveness of the mask, the presence of containment, and the temporal dynamics of adoption. Combined with containment, at least 50% mask adoption can prevent exponential growth of infection. Even if there is a delay in adoption, universal adoption of face masks can prevent new waves of COVID-19.

Stutt, R. O., Retkute, R., Bradley, M., Gilligan, C. A., & Colvin, J. (2020). A modeling framework to assess the likely effectiveness of facemasks in combination with 'lock-down' in managing the COVID-19 pandemic. Proceedings of the Royal Society A, 476(2238), 20200376.

A quantitative transmission model estimating the baseline reproduction rate (R0) of COVID-19 under certain health conditions, such as testing and isolation, contact tracing and quarantine, social distancing, mask-wearing, and other interventions at the individual level. Implementing these strategies in parallel multiplies their effects on reducing reproductive rates. A 96% mask adoption rate alone can prevent exponential growth. Combined with contact tracing, 70% adoption of face masks can slow exponential growth even in the most affected countries. Contact tracing here refers to an action that manages to trace at least 60% of contacts and isolate them within 4 days.

Tian, L., Li, X., Qi, F., Tang, Q., Tang, V., Liu, J., Li, Z., Cheng, X., Li, X., Shi, Y., Liu, H., & Tang, L. (2020). Calibrated Intervention and Containment of the COVID-19 Pandemic. arXiv: Populations and Evolution.

According to a recent meta-analysis, the wearing of the hand-made cotton mask is associated with protection against SARS with a chance ratio of 0.33, which corresponds to a relative risk decreased from 45% to 60% for a total risk of catching the disease between 20% and 60%.

Chu, D. K., Akl, E. A., Duda, S., Solo, K., Yaacoub, S., Schünemann, H. J., ... & Hajizadeh, A. (2020). Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 andCOVID-19: a systematic review and meta-analysis. The Lancet.

Further reading

Do I have to wear a mask if I don't have any symptoms?

Do I have to wear a mask if I already had COVID-19?

Do I have to wear a mask inside / outside?

Can a mask be "worse than nothing"?

What is a superspreader event for COVID-19 ?

Lethality, mortality, excess mortality, R0, kappa: what are we talking about?

Why are superspreader events crucial to understanding the COVID-19 epidemic?

Why is it recommended not to wear a surgical mask for more than 4 hours?

At what age should children wear a mask at school, depending on the country?