The new determination of the National Health Surveillance Agency (Anvisa), which provides for the return of the mandatory mask in airports and planes from Friday (25), goes against what scientific studies have pointed out about the effectiveness of the item as a protective measure against the new coronavirus and its subvariants. In November 2021, Cochrane, a respected medical organization, reviewed
- studies to respect and concluded that masks make little or no difference in the number of people who become infected with respiratory diseases such as Covid. Even if they are special masks like N.
Months earlier, a Danish study, published in Annals of Internal Medicine, involved almost five thousand people and found no difference in Covid infections between the masked group and the maskless group . Cautious, the authors, led by Kasper Iversen, from the University Hospital of Copenhagen, say that their results are inconclusive.
At the beginning of this year, it appeared in the journal Science a randomized controlled trial (RCT) that was considered by many scientists to demonstrate the effectiveness of masks. Conducted in Bangladesh by Yale researchers, the study involved 330 1,000 people in 572 villages rural areas and showed a reduction of
% of symptomatic and infected people with the use of fabric and surgical masks. However, there are still many doubts about the methodological probity of this research.
Despite the apparent large sample, the difference between infected and non-infected groups was minuscule, only 20 people. Furthermore, individuals were not distributed at random, but villages. Other problems were pointed out: researchers only knew about infections if those infected voluntarily reported them. That is, if few infected people who were in the mask group preferred not to report their mild symptoms, the study would already be invalidated. Other problems were pointed out in a scholarly publication that essentially brought the Bangladeshi RCT into disrepute.
Lacks scientific rigor
Although there is other research indicating that the use of masks is effective in stopping infections, such as one recently carried out with children in schools in Boston, in the USA, still lacks a higher standard of scientific rigor. In science, it is rare that false hypotheses do not have any evidence supporting them. Thus, the priority should be on judging the quality of the available evidence.
Medical studies deal with evidence that has different degrees of rigor and quality. From the lowest rigor to the highest, which lead from the most uncertain to the firmest results, they can be classified into:
2022Observational studies: compare at least two groups, one with treatment and the other without, but without interfering on how these groups organized themselves. (Variable degree of safety, but generally low or moderate.)
There are other extra levels of rigor that can be added to a controlled study and randomized, how to create a third group that receives a treatment that is known to be inert — in the case of masks, it could be a group with crocheted masks with large holes for the virus to pass through. In addition, the degree of confidence in the results increases even more if there is a way to encrypt the treatment, so that both the participants and the researchers do not know whether the treatment received is the placebo or the real treatment investigated by the study.
The study with the Boston schools is observational, therefore, it does not have the highest standard of rigor of RCTs. In their absence, one way of trying to improve the quality of evidence to make decisions is to work on study reviews, as Cochrane did last year.
When mask use is recommended?
From his experience in clinical practice and research, Cornell University physician Paul Fenyves knows that the quality of evidence in favor of masks is low. For himself, he relies on his personal experience, a kind of “self-case study”. “For two years, I wore the mask and shared small offices with Covid patients who were coughing, and I never got sick. When I finally contracted Covid in April 2022, it was the way I get all my respiratory infections: from my children”, he told the blog Sensible Medicine.
In voluntary decisions, such as his, low-quality evidence may be appropriate. However, in recommendations of municipal and state health departments or in determinations of agencies, such as Anvisa, more scientific rigor is needed as a basis.
The doctor guided his action by empirical reasons, such as knowing that the pores of special masks such as PFF2 and N95 make it difficult for the pandemic virus, which is transmitted through the air, to pass through. Other doctors with the same knowledge, however, caught Covid despite the same precaution.
It is important to remember that the World Health Organization, for example, started to recommend masks at the beginning of the pandemic when many of its advisors they mistakenly believed that the virus needed large watery droplets to transmit, which would be more easily blocked by masks. An expert demonstrated that the transmission of Covid was through the air, and corrected the premise that led the WHO to error and that had already affected medicine by 60 years.
In the United States, too, the reinstitution of masks has been proposed in some places, especially for children in schools. “So far, this proposal is not gaining much traction even in most pro-mask cities,” says Fenyves. For him, the Centers for Disease Control (CDC) in the country “made an overdose of interventions”, with the effect of “removing even many of their adherents”. Accustomed to adjusting his prescriptions according to his patients’ needs, he extends his criticism of the CDC’s stance on widespread pediatric vaccination against Covid, which is not recommended in countries such as Norway and Denmark.
“We have the American people asking for a less aggressive approach, but the CDC recommending the more aggressive approach”, laments the doctor. For him, this aggressive stance explains the hesitation of many about the use of masks and even about vaccines for Covid, which should be optional for children and not objects of a more energetic stance on the part of the authorities, as is justifiable in cases of immunizers such as BCG and polio vaccines, for example.
Masks could be welcome as a recommendation for people already infected, with symptoms, to reduce the amount of virus they spread in environments through which pass. It is now clear that the most authoritarian measures lead to poor health outcomes, such as low population immunization. The real contribution of the Bangladeshi study, therefore, was to have shown that an educational campaign was more effective than the obligation established by the government to gain adherence.
