How might an evolving understanding of virus transmission affect mask recommendations?

It is fair to say that there has been a lot of contradictory guidelines and information about the use of face masks at a community level. While the WHO are not currently encouraging the universal use of masks among healthy adults in all public settings, we have already seen several nations promoting or mandating the use of masks among the general population (e.g. USA, Czech Republic, China). See this map for a global view of current guidelines (compiled by a pro-mask advocacy group). It is possible that recommendations around masks will change in the coming weeks or months. Below we explain how new evidence may result in changes to recommendations.

Realisation that all citizens pose a risk for transmission - It is now understood that people who are not showing symptoms can still be carrying the virus and can transmit it. This poses a challenge for interrupting transmission as healthy individuals are less likely to take precautionary measures such as quarantining after potential contact with the virus or an infected person. Mask usage among the general population may therefore be considered beneficial for source control. The relative importance of transmission from asymptomatic or pre-symptomatic individuals, compared to transmission via symptomatic individuals, is unclear and still being investigated.

Further evidence around airborne transmission - If further evidence is found to demonstrate that transmission can occur via small airborne droplets (aerosols), mask use will be an important method of reducing transmission in public settings. The WHO does not currently consider airborne transmission via aerosols to be a main route of transmission for SARS-CoV-2 among the general population but has recently acknowledged that it cannot be ruled out in crowded indoor settings with poor ventilation. For more information on the evidence for airborne transmission, read the ‘Mixed evidence of modes of transmission’ section here.

Want to learn more about mask use for interrupting the spread of COVID-19?

• How could wearing a mask reduce COVID-19 transmission?

• What types of masks are there and what are they designed to do?

• What is a N95 respirator and who should use one?

• What is a surgical mask and who should use one?

• What is a fabric mask, who should use one, and how should they be made?

• What should be considered when making fabric masks?

• Hygienic use of fabric face masks

• What is an occupational mask and who should wear one?

• Why doesn’t the WHO recommend that everyone wears face masks in all settings?

• What do we know about the effectiveness of masks to prevent and COVID-19 transmission in community settings?

• What can modelling studies tell us about the effectiveness of wearing masks?

• How well do masks work under laboratory (experimental) conditions?

• Do homemade masks increase the risk of respiratory disease?

• Should hygiene promotion staff wear masks to protect themselves and others?

Editor's note

Author: Jackie Knee
Review: Peter Winch, Julie Watson
Last update: 06.18.2020