Difference between revisions of "Principles and assumptions for using masks during the COVID-19 pandemic"

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# There is no evidence available that supports the implication that masks may be actively harmful
 
# There is no evidence available that supports the implication that masks may be actively harmful
 
# WHO guidance recognises some benefit to mask-wearing by members of the public, both to prevent the wearer from spreading disease to others, and to protect the wearer, but does not endorse mass mask-wearing
 
# WHO guidance recognises some benefit to mask-wearing by members of the public, both to prevent the wearer from spreading disease to others, and to protect the wearer, but does not endorse mass mask-wearing
# However, presymptomatic and asymptomatic transmission ''is'' recognised as a concern in influenza-like viruses, and in such situations [https://www.who.int/influenza/publications/public_health_measures/publication/en/ the WHO has cautiously endorsed mask-wearing]
+
# However, presymptomatic and asymptomatic transmission ''is'' recognised as a concern in influenza-like viruses, and in such situations the WHO has cautiously endorsed mask-wearing{{cite|WHO. Non-pharmaceutical public health measures for mitigating the risk and impact of epidemic and pandemic influenza. October 2019|external|https://www.who.int/influenza/publications/public_health_measures/publication/en/}}
# Other infectious disease experts, such as [https://www.sciencemag.org/news/2020/03/not-wearing-masks-protect-against-coronavirus-big-mistake-top-chinese-scientist-says George Fu Gao] of the Chinese CDC, have long taken the position that masks should be worn by asymptomatic people in public/close-contact situations
+
# Other infectious disease experts, such as George Fu Gao of the Chinese CDC{{cite|Jon Cohen. Not wearing masks to protect against coronavirus is a ‘big mistake,’ top Chinese scientist says. Science Mag, March 2020|external|https://www.sciencemag.org/news/2020/03/not-wearing-masks-protect-against-coronavirus-big-mistake-top-chinese-scientist-says}}, have long taken the position that masks should be worn by asymptomatic people in public/close-contact situations
# There is evidence that the [https://wwwnc.cdc.gov/eid/article/26/6/20-0357_article virus can be spread before symptoms develop], and may also be spread by [https://www.bmj.com/content/368/bmj.m1165 people who never show symptoms], and that presymptomatic/asymptomatic people carry an [https://www.cdc.gov/mmwr/volumes/69/wr/mm6913e1.htm equally high] [https://www.nejm.org/doi/full/10.1056/NEJMc2001737 viral load]
+
# There is evidence that the virus can be spread before symptoms develop{{cite|Zhanwei Du et al. Serial Interval of COVID-19 among Publicly Reported Confirmed Cases. Emerging Infectious Diseases, June 2020 (early release)|external|https://wwwnc.cdc.gov/eid/article/26/6/20-0357_article}}, and may also be spread by people who never show symptoms{{cite|Michael Day. Covid-19: identifying and isolating asymptomatic people helped eliminate virus in Italian village. BMJ 2020.|external|https://www.bmj.com/content/368/bmj.m1165}}, and that presymptomatic/asymptomatic people carry an equally high viral load{{cite|Anne Kimbal et al. Asymptomatic and Presymptomatic SARS-CoV-2 Infections in Residents of a Long-Term Care Skilled Nursing Facility — King County, Washington, March 2020. MMWR Morbidity Mortal Weekly Report, 2020.|external|https://www.cdc.gov/mmwr/volumes/69/wr/mm6913e1.htm}}{{cite|Lirong Zou et al. SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients. New England Journal of Medicine, 2020.|external|https://www.nejm.org/doi/full/10.1056/NEJMc2001737}}
# Public Health England states that there is [https://www.gov.uk/government/publications/covid-19-stay-at-home-guidance/stay-at-home-guidance-for-households-with-possible-coronavirus-covid-19-infection#facemasks ‘very little evidence of'] that masks provide a benefit outside of clinical settings; however, other measures such as respiratory etiquette and hand hygiene are [https://apps.who.int/iris/bitstream/handle/10665/329438/9789241516839-eng.pdf equally poorly evidenced as a public health response] to respiratory infections, and sometimes show [https://www.ncbi.nlm.nih.gov/pubmed/20297744 no benefit in community settings]
+
# Public Health England states that there is ‘very little evidence' that masks provide a benefit outside of clinical settings{{cite|Public Health England. Stay at home: guidance for households with possible coronavirus (COVID-19) infection, April 2020.|external|https://www.gov.uk/government/publications/covid-19-stay-at-home-guidance/stay-at-home-guidance-for-households-with-possible-coronavirus-covid-19-infection#facemasks}}; however, other measures such as respiratory etiquette and hand hygiene are equally poorly evidenced as a public health response to respiratory infections{{cite|WHO. Non-pharmaceutical public health measures for mitigating the risk and impact of epidemic and pandemic influenza. 2019.|external|https://apps.who.int/iris/bitstream/handle/10665/329438/9789241516839-eng.pdf}}, and sometimes show no benefit in community settings{{cite|EL Larson et al. Impact of non-pharmaceutical interventions on URIs and influenza in crowded, urban households. Public Health Reports, 2020.|external|https://www.ncbi.nlm.nih.gov/pubmed/20297744}}
 
# Any individual infection-control measure can create a false sense of security if not presented as part of a package, and masks are no different in this respect
 
# Any individual infection-control measure can create a false sense of security if not presented as part of a package, and masks are no different in this respect
# Masks are '''not an alternative to social distancing''', but they do still significantly reduce the [https://www.researchgate.net/publication/258525804_Testing_the_Efficacy_of_Homemade_Masks_Would_They_Protect_in_an_Influenza_Pandemic ability of the wearer to emit infectious droplets] in situations where distancing cannot be maintained
+
# Masks are '''not an alternative to social distancing''', but they do still significantly reduce the ability of the wearer to emit infectious droplets in situations where distancing cannot be maintained{{cite|Anna Davies et al. Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic? Disaster Medicine and Public Health Preparedness, August 2013.|external|https://www.researchgate.net/publication/258525804_Testing_the_Efficacy_of_Homemade_Masks_Would_They_Protect_in_an_Influenza_Pandemic}}
  
 
==Principles specific to cloth masks==
 
==Principles specific to cloth masks==
# Some authorities, such as the [https://www.ecdc.europa.eu/sites/default/files/documents/Cloth-face-masks-in-case-shortage-surgical-masks-respirators2020-03-26.pdf European Centre for Disease Control] claim that cloth masks ‘may increase the risk of infection’; however, this appears to be derived from [https://bmjopen.bmj.com/content/bmjopen/5/4/e006577.full.pdf one study] which does not, in fact, provide any evidence for whether cloth masks are beneficial or harmful when there is no better alternative
+
# Some authorities, such as the European Centre for Disease Control claim that cloth masks ‘may increase the risk of infection’{{cite|ECDC. Cloth masks and mask sterilisation as options in case of shortage of surgical masks and respirators. March 2020.|external|https://www.ecdc.europa.eu/sites/default/files/documents/Cloth-face-masks-in-case-shortage-surgical-masks-respirators2020-03-26.pdf}}; however, this appears to be derived from one study{{cite|C Raina MacIntyre et al. A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ Open, 2015.|external|https://bmjopen.bmj.com/content/bmjopen/5/4/e006577.full.pdf}} which does not, in fact, provide any evidence for whether cloth masks are beneficial or harmful when there is no better alternative
# Tightly woven cotton cloth does have some ability to block even fine aerosol particles, though only about [https://www.researchgate.net/publication/258525804_Testing_the_Efficacy_of_Homemade_Masks_Would_They_Protect_in_an_Influenza_Pandemic 50% of these]
+
# Tightly woven cotton cloth does have some ability to block even fine aerosol particles, though only about 50% of these{{cite|Anna Davies et al. Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic? Disaster Medicine and Public Health Preparedness, August 2013.}}
# One study has found that [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2440799/ homemade masks gave a protection factor] of 2-3 against aerosol particles,  whereas surgical masks had a protection factor of 4-5 (as compared to a no-mask baseline of 1)
+
# One study has found that homemade masks gave a protection factor of 2-3 against aerosol particles,  whereas surgical masks had a protection factor of 4-5 (as compared to a no-mask baseline of 1){{cite|Marianne van der Sande, Peter Teunis and Rob Sabel. Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population. PLoS One, 2008.|external|https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2440799/}}
# There are some suggestions that a higher level of exposure [https://www.cebm.net/covid-19/sars-cov-2-viral-load-and-the-severity-of-covid-19/ may result in a more severe illness], though at the time of writing this is still uncertain
+
# There are some suggestions that a higher level of exposure may result in a more severe illness{{cite|Carl Heneghan, Jon Brassey and Tom Jefferson. SARS-CoV-2 viral load and the severity of COVID-19. CEBM, 2020.|external|https://www.cebm.net/covid-19/sars-cov-2-viral-load-and-the-severity-of-covid-19/}}, though at the time of writing this is still uncertain
 
# Even when cloth masks are unable to fully protect against infection, it’s still possible that they may have some value by reducing the level of initial exposure to the virus
 
# Even when cloth masks are unable to fully protect against infection, it’s still possible that they may have some value by reducing the level of initial exposure to the virus
 
# Cloth masks are therefore likely better than nothing as protection from contracting COVID-19, during unavoidable close-contact situations
 
# Cloth masks are therefore likely better than nothing as protection from contracting COVID-19, during unavoidable close-contact situations
 
# Surgical masks are clearly a better option for people caring for infected individuals, whenever these are available
 
# Surgical masks are clearly a better option for people caring for infected individuals, whenever these are available
 
# In order to preserve the limited supplies of surgical masks, cloth could have value for general community use by asymptomatic people as source control, to reduce the spread of infection to others
 
# In order to preserve the limited supplies of surgical masks, cloth could have value for general community use by asymptomatic people as source control, to reduce the spread of infection to others

Revision as of 06:40, 23 April 2020

This resource is a draft - it is undergoing review to fact check and improve it prior to adoption. It should only be used if you cannot find other options, and you should err on the side of caution while using it.
This page is specific to the COVID-19 pandemic. Our covid protocol still focuses on somewhat older science relating to droplet transmission. We are currently reviewing this. It will be updated rapidly.

Principles for masks in general

  1. There is currently a severe shortage of masks in the UK, and thus a need to prioritise these for (formal or informal) healthcare workers
  2. This pragmatic question of availability is distinct from the question of whether the wider use of surgical masks would be valuable
  3. There is no evidence available that supports the implication that masks may be actively harmful
  4. WHO guidance recognises some benefit to mask-wearing by members of the public, both to prevent the wearer from spreading disease to others, and to protect the wearer, but does not endorse mass mask-wearing
  5. However, presymptomatic and asymptomatic transmission is recognised as a concern in influenza-like viruses, and in such situations the WHO has cautiously endorsed mask-wearing[1]
  6. Other infectious disease experts, such as George Fu Gao of the Chinese CDC[2], have long taken the position that masks should be worn by asymptomatic people in public/close-contact situations
  7. There is evidence that the virus can be spread before symptoms develop[3], and may also be spread by people who never show symptoms[4], and that presymptomatic/asymptomatic people carry an equally high viral load[5][6]
  8. Public Health England states that there is ‘very little evidence' that masks provide a benefit outside of clinical settings[7]; however, other measures such as respiratory etiquette and hand hygiene are equally poorly evidenced as a public health response to respiratory infections[8], and sometimes show no benefit in community settings[9]
  9. Any individual infection-control measure can create a false sense of security if not presented as part of a package, and masks are no different in this respect
  10. Masks are not an alternative to social distancing, but they do still significantly reduce the ability of the wearer to emit infectious droplets in situations where distancing cannot be maintained[10]

Principles specific to cloth masks

  1. Some authorities, such as the European Centre for Disease Control claim that cloth masks ‘may increase the risk of infection’[11]; however, this appears to be derived from one study[12] which does not, in fact, provide any evidence for whether cloth masks are beneficial or harmful when there is no better alternative
  2. Tightly woven cotton cloth does have some ability to block even fine aerosol particles, though only about 50% of these[10]
  3. One study has found that homemade masks gave a protection factor of 2-3 against aerosol particles, whereas surgical masks had a protection factor of 4-5 (as compared to a no-mask baseline of 1)[13]
  4. There are some suggestions that a higher level of exposure may result in a more severe illness[14], though at the time of writing this is still uncertain
  5. Even when cloth masks are unable to fully protect against infection, it’s still possible that they may have some value by reducing the level of initial exposure to the virus
  6. Cloth masks are therefore likely better than nothing as protection from contracting COVID-19, during unavoidable close-contact situations
  7. Surgical masks are clearly a better option for people caring for infected individuals, whenever these are available
  8. In order to preserve the limited supplies of surgical masks, cloth could have value for general community use by asymptomatic people as source control, to reduce the spread of infection to others
  1. WHO. Non-pharmaceutical public health measures for mitigating the risk and impact of epidemic and pandemic influenza. October 2019
  2. Jon Cohen. Not wearing masks to protect against coronavirus is a ‘big mistake,’ top Chinese scientist says. Science Mag, March 2020
  3. Zhanwei Du et al. Serial Interval of COVID-19 among Publicly Reported Confirmed Cases. Emerging Infectious Diseases, June 2020 (early release)
  4. Michael Day. Covid-19: identifying and isolating asymptomatic people helped eliminate virus in Italian village. BMJ 2020.
  5. Anne Kimbal et al. Asymptomatic and Presymptomatic SARS-CoV-2 Infections in Residents of a Long-Term Care Skilled Nursing Facility — King County, Washington, March 2020. MMWR Morbidity Mortal Weekly Report, 2020.
  6. Lirong Zou et al. SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients. New England Journal of Medicine, 2020.
  7. Public Health England. Stay at home: guidance for households with possible coronavirus (COVID-19) infection, April 2020.
  8. WHO. Non-pharmaceutical public health measures for mitigating the risk and impact of epidemic and pandemic influenza. 2019.
  9. EL Larson et al. Impact of non-pharmaceutical interventions on URIs and influenza in crowded, urban households. Public Health Reports, 2020.
  10. 10.0 10.1 Anna Davies et al. Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic? Disaster Medicine and Public Health Preparedness, August 2013.
  11. ECDC. Cloth masks and mask sterilisation as options in case of shortage of surgical masks and respirators. March 2020.
  12. C Raina MacIntyre et al. A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ Open, 2015.
  13. Marianne van der Sande, Peter Teunis and Rob Sabel. Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population. PLoS One, 2008.
  14. Carl Heneghan, Jon Brassey and Tom Jefferson. SARS-CoV-2 viral load and the severity of COVID-19. CEBM, 2020.