By Andrea Hargraves 
This Tuesday (17), the Attorney General’s Office (PGR) sent a statement to the Supreme Court (Supreme Court) saying that there is no scientific evidence to support the use of face protection masks as an effective means of controlling and preventing the SARS virus. – Corona virus infection.
The text, signed by the Deputy Prosecutor General of the Republic, Lindora Araujo, states that studies on the effectiveness of the masks are “only observational and epidemiological” and would not, therefore, be strong scientific evidence.
But even observational studies, in a scientific context, are important and serve as sources of evidence, whether or not in favor of a hypothesis or a research object.
In the case of specific masks, the knowledge about their protection against infection is already strong, produced from numerous scientific studies, as well as examples from countries that have adopted Mass use of masks Since the beginning of the epidemic, they have succeeded in controlling the cases.
Here are some of the claims made by PGR that are not scientifically based.
“It can’t be said [o uso da máscara] really leave To prevent the entry or spread of Covid.”
Several studies have already demonstrated how masks, especially those that are more modified for the face and have better filtration, such as N95 or PFF2, are effective in preventing infection with the SARS-CoV-2 coronavirus.
The protective ability of masks varies depending on the type of material used and the fabric. A study conducted by the USP evaluated the filtration efficiency of different types of masks sold in Brazil and found that N95 or PFF2 masks were the most suitable, with efficiency above 98%, followed by TNT or surgical masks (between 80% and 90%) and finally hair cloth with 40%. Knit masks with open weaves or synthetic fabrics such as Lycra and microfibers are not effective in protection (about 15%).
Other research conducted in the United States indicated an efficacy of up to 95% when combining a surgical mask under a cloth mask. These values indicate the ability of direct masks to filter the air and retain viral particles.
In addition to research on the filtration efficiency of masks, another study published in Physics of Fluids evaluated how masks and face shields form a physical barrier to potentially contaminated air.
In the analysis, the scientists simulated coughs and sneezes using a mannequin with a nose and mouth covered with different types of protection: homemade masks, simple surgical masks, transparent masks, and N95 or PFF2 type masks with or without an exhalation valve.
The results of the research confirmed the effectiveness of PFF2 masks in retaining most particulates. However, the small plane escaping from the top of the mask spreads out for a short distance.
In the case of homemade masks or face shields (without a mask underneath), the protection is much lower, with the air jet spreading up to 4 metres. This proves the ability of N95 masks to prevent the spread of the virus in the environment, and this ability is reduced because the material used is more open.
Finally, a study was published in December 2020 in Journal of Aerosol Science and Technology CDC scientists have shown that masks made of three layers of cotton have the ability to stop 51% of the aerosols that a person can expel if they cough, while the blockage caused by a surgical mask is 59%.
“IThere are no scientific studies with a high degree of reliability on the level of effectiveness of the protective measure.
Evidence in favor of the use of masks for personal protection and for preventing the spread of viral particles in the air, has already been substantiated by both observational, case-control and experimental studies.
There is scientific consensus today that the main route of transmission of the Corona virus is the air, not contaminated surfaces. Thus, masks directly protect, as a physical barrier against saliva droplets released when speaking, coughing or sneezing, as well as filtering air that may be full of aerosol particles (invisible to the naked eye) containing the virus.
A study published in April 2020 in the Journal of the American Chemical Society evaluated the filtration efficacy of household masks made of different fabrics, indicating that the average overall protection is over 50%.
However, the main finding was that the key to preventing the spread of aerosols was fit to the face – even a small hole of less than 1 cm can reduce the effectiveness of any mask, including N95 or PFF2, by up to two-thirds.
Already a systematic review published in the American Journal PNAS In January 2021, it provided strong evidence in favor of the mass use of masks as a measure to control transmission of the virus in the community.
Finally, a study It was published in Science in June 2021 evaluating, through models, the effectiveness of face masks in high transmission situations (eg hospitals) compared to those with less virus in the air (most real-life situations, such as outdoor activities). in the fresh air). In both cases, the use of masks, both surgical and PFF2 type, reduced the chance of infection, and the reduction was greater if there was blanket use of a face shield.
“Rigorous testing cannot be done to prove the exact measure of a protective mask’s effectiveness as a means of preventing the spread of the novel coronavirus.“
What is not possible in this case are the so-called randomized, controlled, double-blind clinical trials (the so-called gold standard in evidence-based medicine studies). These studies may be unethical and will not be able to eliminate factors that could influence the outcome, such as the type of activity each person is exposed to and proper mask use.
But the fact that this particular type of clinical trial cannot be conducted does not mean that the studies that have been done to evaluate the effectiveness of masks are not rigorous.
In vitro research and evaluation models indicate a high protection of the masks to contain the spread of the virus. This ability is especially important for indoor environments, but this does not mean that the danger in the outdoor environment is zero. Aerosol particles can remain in the air for up to three hours, and transmission can occur from inhalation of contaminated air.
Existing studies on protective mask efficacy are only observational and epidemiological studies.
The fact that current studies on the effectiveness of masks when used globally are mostly observational or epidemiological does not detract from their importance or merit.
First, this question is based on one of the principles of scientific methodology which states that the association (which can be cause and effect, relationship, etc.) between two factors can only be observed in a controlled experiment. This can be one, but not the only, means of accepting or disproving a scientific hypothesis.
In general, this type of controlled study is used to evaluate the effectiveness of a drug in preventing disease, as the control group does not receive the drug. Since drugs can have toxicity, side effects, and other effects in the body, it is easier to assess the effect of a drug and what not.
In the case of protective equipment, it is not possible to use a control group, as it would be unethical to send a study volunteer to a dangerous situation. The logic is the same for other protective gear such as helmets or parachutes. In these cases, laboratory trials simulating use cases are sufficient to establish its safety and efficacy.
On the other hand, population studies can assess the medium to long-term effects of a measure or intervention. In general, the robustness of these studies is given by robust statistical analysis and adjustment for uncontrolled variables such as gender, age, and other demographic characteristics.
“The World Health Organization recognizes, however, that in addition to face masks, other preventive measures must be taken together”
Non-pharmacological preventive measures should be used in combination, but this does not mean that they are ineffective in isolation. Several studies have already shown how a combination of measures, including social distancing, closures and the use of masks, are effective in reducing cases and deaths from Covid-19.
The success in conducting a pandemic in many countries in the first year of the epidemic, thanks to the combination of measures taken by the government and the population as a whole, underscores the importance of social distancing, control and tracing of cases, and the use of masks to prevent the spread of the virus.