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Should individuals in the community without respiratory symptoms wear facemasks to reduce the spread of COVID-19?

Published

This is a rapid review of the knowledge base for using face mask, by people in the community to reduce the spread of covid-19.

Forside omslag notat covid-19 face mask  community_ENG.jpg

This is a rapid review of the knowledge base for using face mask, by people in the community to reduce the spread of covid-19.


Key message

Health authorities have given conflicting recommendations regarding the use of facemasks by asymptomatic individuals in the community to reduce the spread of COVID-19. For example, the World Health Organization (WHO) states that “at present, there is no direct evidence (from studies on COVID-19 and in healthy people in the community) on the effectiveness of universal masking of healthy people in the community to prevent infection with respiratory viruses, including COVID-19”. Yet, “WHO has updated its guidance to advise that to prevent COVID-19 transmission effectively in areas of community transmission, governments should encourage the general public to wear masks in specific situations and settings as part of a comprehensive approach to suppress SARS-CoV-2 transmission”. This includes settings where individuals are unable to keep a physical distance of at least 1 meter. WHO is also strongly encouraging countries to conduct research on this critical topic.

An Evidence to Decision (EtD) framework was used to guide the process from reviewing the evidence to a recommendation. An evidence base was made by a structured literature review using the L·OVE COVID-19 database and a living COVID-19 evidence map. Relevant ongoing reviews and studies were searched for in PROSPERO, the list of COVID-19 trials in the International Clinical Trials Registry Platform (ICTRP) (updated 12 May 2020) and ClinicalTrials.gov COVID-19 list. Additional articles were identified by checking the references in retrieved articles and personal contacts.

There is evidence of a protective effect of medical facemasks against respiratory infections in community settings. However, study results vary greatly. Randomised trials from community settings indicate a small protective effect. Laboratory studies indicate a larger effect when facemasks are used by asymptomatic but contagious individuals to prevent the spread of virus to others, compared to use by uninfected individuals to prevent themselves from becoming infected. Because incorrect use of medical facemasks limits their effectiveness, countrywide training programmes adapted to a variety of audiences would be needed to ensure the effectiveness of medical facemasks for reducing the spread of COVID-19. It is not known whether the use of medical facemasks would be widely accepted by the healthy population in Norway, or the extent to which correct use could be achieved. 

Non-medical facemasks include a variety of products. There is no reliable evidence of the effectiveness of non-medical facemasks in community settings. There is likely to be substantial variation in effectiveness between products. However, there is only limited evidence from laboratory studies of potential differences in effectiveness when different products are used in the community. 

Given the low prevalence of COVID-19 currently, even if facemasks are assumed to be effective, the difference in infection rates between using facemasks and not using facemasks would be small. Assuming that 20% of people infectious with SARS-CoV-2 do not have symptoms, and assuming a risk reduction of 40% for wearing facemask, 200 000 people would need to wear facemasks to prevent one new infection per week in the current epidemiological situation.

The undesirable effects of facemasks include the risks of incorrect use, a false sense of security (leading to relaxation of other interventions), and contamination of masks. In addition, some people experience problems breathing, discomfort, and problems with communication. The proportion of people who experience these undesirable effects is uncertain. However, with a low prevalence of COVID-19, the number of people who experience undesirable effects is likely to be much larger than the number of infections prevented.

An expert panel discussed and assessed the evidence using an explicit set of criteria. The panel did not take into consideration the shortage of medical facemasks. The assessments for each criterion were judged both individually and in a consensus process, and the overall recommendation and report were reviewed by the panel.

Conclusion

In the current epidemiological situation in Norway, wearing facemasks to reduce the spread of COVID-19 is not recommended for individuals in the community without respiratory symptoms who are not in near contact with people who are known to be infected. If the epidemiological situation worsens substantially in a geographical area, the use of facemasks as a precautionary measure should be reconsidered. Measures to reduce risks during necessary public transport and during mass events, including wearing facemasks, should be explored further.

If use of facemasks by individuals without respiratory symptoms in the community is recommended in specific circumstances, such as public transport or mass events, medical masks or quality controlled non-medical masks with a documented filtration effect should be used. National priorities for the use of personal protective equipment may apply, given existing shortages. If any such recommendation is made, the community should be given training to ensure correct use and the risks should be explained, especially the risks of a false sense of security and contamination of masks. The training should be tailored to the needs of different groups, including people with different levels of fluency in Norwegian and different socio-economic circumstances.

Downloadable as PDF. In English. Norwegian summary.

About this publication

  • Year: 2020
  • By: Norwegian Institute of Public Health
  • Authors Iversen BG, Vestrheim DF, Flottorp S, Denison E, Oxman AD.
  • ISBN (digital): 978-82-8406-106-1