Masks have been and continue to be promoted by official bodies in my country – Brazil – by our FDA equivalent (ANVISA) and also by some state governors and city mayors. Masking was mandatory in planes throughout the country until March 1st 2023, and in public transportation in some cities, including São Paulo, the biggest city in Latin America, they are still required. Although from a mechanistic (laboratory experiments) and intuitive point of view masks are plausible interventions, their effectiveness has not been validated in randomized controlled trials (RCTs).
This fact was correctly pointed out by the president of the Brazilian Federal Council of Medicine in a letter to ANVISA, who bravely said: “The use of masks as virtue signaling or as a measure of a sense of social belonging can never be imposed on people who do not share such ideologies or behaviors, especially in the absence of scientific evidence or even possible harm to the patient’s health, as it is in the case at hand.”
The requirement that masks pass through RCTs is not a mere formality; drugs and therapies are rarely approved without one or more RCTs with clear and statistically significant results. The effectiveness of masks in reducing viral transmission was tested in several RCTs before and after the start of the COVID-19 pandemic.
These studies were reviewed and updated by Cochrane researchers in a 300-page paper published in late January 2023. To those who are not familiar with this organization, Cochrane is an international network of collaborators whose mission is to analyze and summarize the best evidence from biomedical research, without interference from commercial and financial interests, and is the leading global advocate for evidence-based health care. Cochrane reviews are internationally recognized as the benchmark for high-quality information.
For 10 years I taught a course on science and pseudoscience to graduate students at the University of São Paulo (USP). Whenever a student asked me “What is a reliable source of clinical and biomedical information?” I answered, without blinking: Cochrane. This was correct well before the advent of the COVID-19 pandemic, and it is still correct today.
Back to the Cochrane review. The paper looked at the effect of various non-pharmacological interventions on respiratory virus transmission, among them medical/surgical masks. The conclusion of the analysis of 13 RCTs, conducted between 2008 and 2022, was that the risk reduction provided by masks, based on laboratory testing for influenza/SARS-CoV-2 was 1.01. The confidence interval, which indicates the variation among the studies analyzed in the review, was 0.72 (28 percent risk reduction) to 1.42 (42 percent risk increase). In other words, for the masks to have any effect, the risk reduction should have been lower than 1.0. The authors thus concluded based on these data (the best scientific evidence available) that masks were found to have no effect on viral transmission.
In fact, the inefficiency of masks had already been pointed out in a previous Cochrane review published in December 2020. Even before that, anyone who had looked at the scientific literature in the field would have deduced the same.
There is a claim made by masking advocates that the science of masks has evolved over the last three years and that cloth masks, medical masks and surgical masks are no longer sufficient. Instead, we should use respirators based on P2/N95 standards. This reasoning, however, has some flaws. To begin with, the overwhelming majority of people use cloth masks or surgical masks, which are much more affordable than respirators.
In addition, the Cochrane review also evaluated 5 RCTs that compared P2/N95 respirators to medical/surgical masks. The pooled risk reduction was 1.10, with a confidence interval of 0.90 to 1.34, meaning that surgical/medical masks performed better than P2/N95 respirators, but the result was not statistically significant.
Furthermore, in December 2022, an RCT comparing the effect of medical masks and N95 respirators against COVID-19 transmission was published. This study, conducted in 29 healthcare facilities in Canada, Israel, Pakistan and Egypt, was the largest RCT on N95 respirators ever conducted. The result was that there was no significant difference between the groups who used N95 and those who used medical masks. In other words, N95 is no better than medical masks. And since we already know that medical masks do not prevent viral transmission….
Real-world data (also called ecological evidence) is another type of analysis that is less rigorous than RCTs but still informative and accessible. For example, I showed in a paper published in April 2022 that Spain and Italy, respectively, had masking rates of 95 percent and 91 percent (the percentage of people who claim to always wear a mask when leaving home), i.e. the highest mask adherence rates in all of Europe during the winter of 2020-2021.
Among 35 European countries analyzed during that time period, Spain and Italy ranked 18th and 20th, respectively, in terms of the number of cases of COVID-19. In theory, if masks prevented viral transmission, the Spanish and Italian populations should have had the lowest case rates of COVID-19, yet that’s not what the data shows.
As another example, Japan, which is known for its high levels of mask use before the pandemic, recorded a 15-fold increase in COVID-19 cases between January 1 and December 31, 2022 (from 1.73 million to 29.23 million cases), even though the use rate of masks has never dropped below 85 percent in this country.
The high level of masking in Japan in the first year of the pandemic was cited as the reason for the low COVID-19 rates there. But Japan’s apparent success in combating COVID-19 was short-lived, and it had nothing to do with masking, as the “experts” would have discovered if they waited a little longer. Although ecological evidence cannot be used to infer causality, it does indicate that at the population level, masks failed as well.
Another point made by some “experts” is that masks are to respiratory viruses, just as condoms are to sexually transmitted diseases (STDs). However, condoms and masks are not comparable, mainly because these two PPEs provide completely different levels of protection. It is not possible to directly test the effect of condoms on STD prevention because of ethical considerations (especially in cases of incurable diseases such as AIDS).
Instead, RCTs have been conducted comparing the effectiveness of latex or other types of condoms in preventing pregnancy. The average effectiveness of traditional latex condoms, from 11 separate studies, was 97.8 percent (50-fold risk reduction). On the other hand, the RCT most favorable to the use of masks, (the Bangladeshi cRCT) showed a risk reduction of only 11.6 percent (1.13-fold). The argument that masks are equivalent to condoms is therefore unconvincing.
Is there scientific evidence that masks are effective at preventing respiratory virus transmission? Yes, there is. But they are all observational studies (or their reviews) of low quality compared to RCTs. The government and media have used these lower quality studies to impose masks on the population.
This point is so important that I will repeat it: masking mandates were passed based on low-quality studies, at the expense of more reliable randomized trials, which demonstrated, in their entirety, that they did not reduce viral transmission in rigorous, well-controlled trials. As a rule, the better the quality of the study (e.g., observational versus randomized trials), the lower the effectiveness of masks. These trials should not be taken as evidence of causality and certainly should not inform public health policy.
On the other hand, effective interventions, such as condoms for preventing pregnancy and STDs, and vaccines and antibiotics for preventing and treating infectious diseases, generally provide robust conclusive results. Take, for example, two Cochrane meta-analyses that examined the use of antibiotics. In one of them, antibiotics were tested for severe pneumonia in children, with success rates of 80-90 percent. Another meta-analysis reviewed the use of antibiotics against rural typhus with success rates of 95-100 percent.
We also saw that condoms have 98 percent efficiency rates.
In contrast, the Cochrane meta-analysis on masks showed zero effect on influenza virus or SARS-CoV-2 transmission! This is why antibiotics and condoms are effective interventions and masks are not.
Given the exposure above, why do some medical authorities still promote mask wearing? A few hypotheses: (1) a physical barrier intuitively confers a sense of safety – even I, who know masks do not protect, feel safer wearing one; (2) mechanistic evidence (laboratory experiments) shows that masks do filter viral particles (although surgical masks or cloth masks, worn by the majority of people, only provide 10 to 12 percent filtration efficiency); (3) insufficient knowledge of the scientific evidence.
Despite the evidence provided by published RCTs and systematic reviews, some authorities continue to claim that more clinical trials should be conducted, but not now… because conducting RCTs during a pandemic would be unethical.
According to this ideological current, the precautionary principle suggests that we use masks, even without knowing whether they work or not. However, it should be remembered that two RCTs of masks were conducted during the COVID-19 pandemic.
Furthermore, all randomized trials conducted to date have consistently shown that masks are ineffective in reducing viral transmission; therefore, including a control group (without masks), even during a pandemic, would most likely pose no risk to study participants.
Masks were promoted as a key tool for reducing or even stopping the spread of SARS-CoV-2 during the COVID-19 pandemic. The wearing of masks in public places is mandated by law in many countries.
However, even before the pandemic, the best available evidence – randomized controlled trials – already showed that masks are ineffective in containing respiratory viral transmission. Additional RCTs conducted during the pandemic support this conclusion. Therefore, the best available evidence does not support even the recommendation of wearing masks, let alone making them compulsory.
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