A hierarchy of evidence (or levels of evidence) is a heuristic used to rank the relative strength of results obtained from scientific research. There is broad agreement on the relative strength of large-scale, epidemiological studies. More than 80 different hierarchies have been proposed for assessing medical evidence.[1] The design of the study (such as a case report for an individual patient or a blinded randomized controlled trial) and the endpoints measured (such as survival or quality of life) affect the strength of the evidence. In clinical research, the best evidence for treatment efficacy is mainly from meta-analyses of randomized controlled trials (RCTs).[2][3] Typically, systematic reviews of completed, high-quality randomized controlled trials – such as those published by the
Cochrane Collaboration – rank as the highest quality of evidence above observational studies, while expert opinion and anecdotal experience are at the bottom level of evidence quality.[2][4]
CDC: On June 4, 2020, the CDC published guidance indicating that masks do not deter the spread of Covid-19 after as little as fifteen minutes of exposure to someone with symptoms. CDC, Public Health Guidance for Community-Related Exposure, updated July 31, 2020.
https://www.cdc.gov/coronavirus/2019-ncov/php/public-health-recommendations.html
WHO: While recommending the wearing of masks for health professionals, the World Health Organization acknowledged that there is no evidence that mask wearing prevents the spread of Covid-19 and that the science simply does not support requiring otherwise healthy people to wear face masks all day.
“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.” World Health Organization (WHO), Advice on the use of masks in the context of COVID-19, Interim Guidance (June 5, 2020) at 6.
https://www.who.int/publications/i/item/advice-on-the-use-of-masks-in-the-community-during-home-care-and-in-healthcare-settings-in-the-context-of-the-novel-coronavirus-(2019-ncov)-outbreak
WHO also acknowledged some of the risks long-term mask use poses to health workers and others:
Medically qualified, UK Correspondent
@BBCNewsnight | 2019 British Journalism Award winner
“We had been told by various sources WHO committee reviewing the evidence had not backed masks but they recommended them due to political lobbying. This point was put to WHO who did not deny. We said some people think we should not wait for RCTs before putting policies in place”
4:25 AM · Jul 12, 2020
The ineffectiveness of face masks in stemming the spread of viral respiratory diseases, including Covid-19, is widely known and acknowledged in the scientific and medical literature and scientific communities. Therefore, it seems that the transition in public health recommendations to promote widespread mask mandates was based on a combination of low-level observational studies, speculative mechanistic studies, fear, and, most of all, POLITICS, NOT SCIENCE.
To clear up the confusion, I will argue that the scientific evidence not only does not support the community wearing of face masks, but the evidence shows that healthy people wearing face masks pose serious health risks to wearers.
https://jamanetwork.com/journals/jama/fullarticle/2749214
- This CDC meta-analysis found that face masks failed to provide a significant reduction to virus transmission.
- “In our systematic review, we identified 10 [Randomly Controlled Trials] that reported estimates of the effectiveness of face masks in reducing laboratory-confirmed influenza virus infections in the community from literature published during 1946–July 27, 2018. In pooled analysis, we found no significant reduction in influenza transmission with the use of face masks.”
- There is limited evidence for their effectiveness in preventing influenza virus transmission either when worn by the infected person for source control or when worn by uninfected persons to reduce exposure. Our systematic review found no significant effect of face masks on transmission of laboratory-confirmed influenza. Mandates for children to wear face masks fails even a rational basis test, and is clearly not in a child's best interest, when assessed through a factual, evidence-based analysis, rather than a fear-based lens. It is simply not rational to believe that face masks will be properly and studiously worn by young children for up to ten hours in a school day. In fact, the overwhelming weight of scientific literature to date establishes that face masks do not prevent the spread of COVID-19 by, to, or from, children. Radonovich, L.J. et al., N95 Respirators vs Medical Masks for Preventing Influenza Among Health Care Personnel: A Randomized Clinical Trial, JAMA. 2019; 322(9): 824–833. doi:10.1001/jama.2019.11645, 2019.
Long, Y. et al., Effectiveness of N95 respirators versus surgical masks against influenza: A systematic review and meta‐analysis, J Evid Based Med. 2020; 1‐ 9.
See e.g., Patrick Saunders-Hastings, et, al., Effectiveness of personal protective measures in reducing pandemic influenza transmission: A systematic review and meta-analysis, Epidemics, v. 20 (September 2017)
An April 2020 review by the Norwich School of Medicine found that “the evidence is not sufficiently strong to support widespread use of face masks”, but supports the use of masks by “particularly vulnerable individuals when in transient higher risk situations.”
Dr. Russell Blaylock, a nationally recognized board-certified neurosurgeon, health practitioner, author, and lecturer warns that not only do face masks fail to protect the healthy from getting sick, but they also create serious health risks to the wearer.
See also Denis G. Rancourt, PhD, Masks Don't Work: A review of science relevant to COVID-19 social policy, Ontario Civil Liberties Association, April 11, 2020.
https://www.ncbi.nlm.nih.gov/pubmed/19216002
- There have been extensive randomized controlled trial (RCT) studies, and meta-analysis reviews of RCT studies, which all show that masks and respirators do not work to prevent respiratory influenza-like illnesses, or respiratory illnesses believed to be transmitted by droplets and aerosol particles. Furthermore, the relevant known physics and biology, which I review, are such that masks and respirators should not work. It would be a paradox if masks and respirators worked, given what we know about viral respiratory diseases: The main transmission path is long residence-time aerosol particles (< 2.5 µm), which are too fine to be blocked, and the minimum-infective-dose is smaller than one aerosol particle. Jacobs, J. L. et al. (2009) Use of surgical face masks to reduce the incidence of the common cold among health care workers in Japan: A randomized controlled trial, American Journal of Infection Control, Volume 37, Issue 5, 417 – 419
Cowling, B. et al., Face masks to prevent transmission of influenza virus: A systematic review, Epidemiology and Infection, 138(4), 449-456. doi:10.1017/S0950268809991658 2010.
bin-Reza et al., The use of masks and respirators to prevent transmission of influenza: a systematic review of the scientific evidence, Influenza and Other Respiratory Viruses 6(4), 257–267, 2012.
Offeddu, V. et al., Effectiveness of Masks and Respirators Against Respiratory Infections in Healthcare Workers: A Systematic Review and Meta-Analysis, Clinical Infectious Diseases, Volume 65, Issue 11, 1 December 2017, Pages 1934–1942.
See Michael Klompas, M.D., M.P.H., et. al., Universal Masking in Hospitals in the Covid-19 Era, New England Journal of Medicine, N Engl J Med 2020; 382:e63 (May 21, 2020).
See also Lisa M Brosseau, ScD, Margaret Sietsema, PhD, COMMENTARY: Masks-for-all for COVID-19 not based on sound data, Center for Infectious Disease Research and Policy, University of Minnesota, April 1, 2020.
In 2016, the Cochrane Collaboration “Wounds Group” revisited the topic of effectiveness of face masks for preventing surgical wound infections again in 2016. In this updated review they added any new studies on the topic that entered the literature since their 2014 review (above).
See, e.g., Neil W. M. Orr, M.D., Mchir, FRCS, Is a mask necessary in the operating theatre?, Annals of the Royal College of Surgeons of England, vol. 63, 1981.
Da Zhou et al., Unmasking the surgeons: the evidence base behind the use of face masks in surgery, Journal of the Royal Society of Medicine; 2015, Vol. 108(6) 223–228.
M.W. Skinner, B.A Sutton, Do Anaesthetists Need to Wear Surgical Masks in the Operating Theatre? A Literature Review with Evidence-Based Recommendations, Anaesthesia and Intensive Care, Vol. 29, No. 4, August 2001.
Naoya Kon, Cloth face masks offer zero shield against virus, a study shows, The Asahi Shimbun, study by Kazunari Onishi.
See Rancourt, Face masks, lies, damn lies, and public health officials: “A growing body of evidence” August 2020.