The use of masks by healthy people in the community has been presented by several agents as one of the most important and effective measures during the pandemic. But, is there strong scientific evidence to attest this effectiveness?
Most systematic reviews that include RCTs (randomized controlled trials), of maximum quality and low bias, point to little or no effect in the containment of respiratory viral diseases.
Several studies of low or medium reliability show inconsistent or contradictory results. This fact is easily understandable given the high bias to which they are subject.
In addition to being unreliable, they are often used to reinforce personal opinions, popular intuition, or even institutional positions, including those of governments and health agencies.
For these reasons, we approach the maximum quality studies (RCTs), the only ones capable of defining reliable causal relationships.
WHO systematic review
We used the recent WHO systematic review (2019) as a starting point, which summarizes the results obtained in this type of studies on masks.
It includes 10 RCTs and reinforces the previous idea that the use of a face mask don´t show “significant effects” on the transmission of the influenza virus or ILI (Influenza-like illness).
Summary conclusions RCTs (Table 7, WHO. Non-Pharmaceutical Public Health Measures to Mitigate the Risk and Impact of Influenza Epidemics and Pandemics , 2019):
Aiello AE, 2010
“Significant reduction in ILI during weeks 4–6 in mask and hand hygiene group compared to control; No significant reduction in ILI in mask and hand group or mask-only group or control.”
Aiello AE, 2012
“No significant reduction in rates of laboratory confirmed influenza in mask and hand group or mask-only group or control group.”
Barasheed O, 2014
“No significant difference in laboratory confirmed influenza in two arms; protective effect against syndromic ILI compared to controls (31% versus 53%, p = 0.04.)”
Cowling BJ, 2008
“No significant reduction in the secondary influenza attack rate in control, mask or hand group.”
Cowling BJ, 2009
“No significant difference in rates of laboratory confirmed influenza in hand-only or mask and hand group.”
Larson EL, 2010
“No significant reduction in rates of laboratory confirmed influenza in control, hand, mask or hand group.”
MacIntyre CR, 2009
“No significant difference in rate of laboratory confirmed influenza in control, face mask or P2 mask group.”
MacIntyre CR, 2016
“Clinical respiratory illness, ILI and laboratory confirmed viral infections were lower in the mask arm compared to control, but results were not statistically significant.”
JM Simmerman, 2011
“No significant reduction in rate of secondary influenza infection in control, hand, mask or hand group.”
Suess (2012) (24)
“No significant difference in rate of laboratory confirmed influenza in control, mask, mask or hand group”
In this document, the WHO points out:
“In the studies of face mask use with or without hand hygiene, the pooled estimate of the risk reduction against laboratory-confirmed influenza was 0.90 (95% CI: 0.75–1.12), which suggests that additional randomized trials would be less likely to identify a substantial protective efficacy of face masks.”
RCT with cloth masks
The only cloth mask RCT (healthcare workers) suggested the possibility of increasing spread.
RCTs published during the pandemic
The published RCT to date that focused on SARS-CoV-2 failed to find statistically relevant differences between the mask (high quality surgical) and control groups.
“Our results suggest that the recommendation to wear a surgical mask outside home, among other people, did not, at conventional levels of statistical significance, reduce the incidence of SARS-CoV-2 infection in mask wearers in an environment where social distancing and other public health conditions were practiced…”
The Cochrane Systematic Review (influenza) update, based on pre-pandemic studies, also concluded that wearing a mask makes little or no difference.
“The combined results of randomized trials did not show a clear reduction in respiratory viral infection with the use of medical/surgical masks during seasonal flu.”
WHO’s current position
WHO Declaration (December 2020):
“At the moment, there is only limited and inconsistent scientific evidence to support the effectiveness of the use of masks by healthy people in the community to prevent infection with respiratory viruses, including SARS-CoV-2.” WHO. Use of masks in the context of Covid-19. Interim guide. December, 2020.
“There is a moderate overall quality of evidence that face masks do not have a substantial effect on influenza virus transmission.” –WHO. Non-pharmaceutical public health measures to mitigate the risk and impact of influenza epidemics and pandemics – quality of evidence. (Page 26, January 2021)
WHO recommendation
The WHO, despite acknowledging “that there is no evidence that it is effective in reducing transmission” states that there is “mechanical plausibility for potential effectiveness”.
Thus, it recommends the use in people without symptoms only in severe epidemics/pandemics. This recommendation takes into account the fact that the organization considers that “significant damage is not anticipated” from this measure.
This recommendation sustained, mainly in the devaluation of the possible negative effects, contradicts the initial position that, in addition to the lack of quality evidence, referred to several associated dangers.
It also contradicts what other health agencies recognize. For example, the ECDC mentions, among other possible negative effects:
– Reuse of masks intended for a single use, with the increased risk of self-contamination;
– Communication difficulties, especially among people with hearing impairment;
– Skin problems;
– Environmental issues.
Final ideas
Despite the sudden change in position on masks from numerous health agencies and public health officials, no quality evidence has emerged to support this change. The two RCTs, published in the meantime, go in the same direction as the previous ones.
Nevertheless, in many countries, countless media protagonists, experts or not, continue to transmit the idea that masks are the most effective (or even indispensable) tools to reduce infections, without having scientific evidence on their side.
Supporting public policy, and an entire media agenda, on studies with a low level of evidence (such as laboratory or observational studies) or personal opinions, which contradict previous and even more recent robust evidence, is at the very least risky. Namely, because it may be giving a “false sense of security” and causing negative effects, without the promised benefits.
Inexplicably, there seems to be little effort to substantiate some of the new assumptions with RCTs, for example, between user and non-user groups in the community or between schools with different policies regarding mask use.
Attachments
Figure 3, 4 – WHO. Non-pharmaceutical public health measures to mitigate the risk and impact of influenza epidemics and pandemics – quality of evidence . Page 26. 2019.
