The largest and most rigorous study on the effects of the mask when it comes to containing the coronavirus in populations confirms what scientists have been saying for months: they work.
The debate on the outdoor mask: a more cosmetic than useful measure to stop the fifth wave
Although masks have been one of the great protagonists of the pandemic, their mandatory use for the general population in many countries of the world generated and continues to generate great controversy. The limited quantity and quality of scientific studies on masks in the real world has not helped to dispel some of this controversy. Unlike the investigation of the usefulness of treatments or vaccines against COVID-19, whose efficacy is relatively easy to know in clinical trials, the use of masks at the community level faces important biases and complications that make it difficult to know their true usefulness for limit the spread of SARS-CoV-2.
The main complication when it comes to knowing the true mask efficacy to control epidemics of respiratory infectious diseases arises from the same mechanism of action of these garments for the face: blocking both the entry and exit of droplets and respiratory aerosols with infectious agents through the mask. Thus, to correctly assess the usefulness of masks, it is not enough to study only the people who use them, but it is also necessary to include the individuals in contact with the previous ones who could have less risk of contagion because the former use face mask.
In other words, investigating in the most rigorous way possible the true value of masks in limiting contagions in the real world is a great scientific challenge, since it involves studying a considerable number of people within a community. And, even despite achieving the above, there would continue to be other factors that hinder this task: the different degree of involvement when using the mask, its correct or incorrect use, the possible association with other protective or risk behaviors. ..
The most powerful and rigorous study yet
On August 31, a preliminary article (preprint), not yet reviewed by experts in the field or published in a scientific journal, with the results of the largest randomized controlled trial to date to find out the effect of promoting the use of masks in limiting coronavirus infections in populations. This gigantic study covers more than 342,000 adults from 600 villages in Bangladesh and was conducted between November 2020 and April 2021. About 163,000 people were in the control group, in which no intervention was performed. In the other group, of 178,000 individuals, different actions were carried out to promote the use of masks (surgical or cloth) in the community.
From the results of a previous study, the researchers selected the most effective measures to increase mask use among the general population of selected villages in Bangladesh. As the study’s first author, Jason Abaluck, a professor of economics at Yale University, explains, the strategy consisted of four actions: distribute masks for free, provide information on their usefulness, reinforce their use in public through individuals asking people who did not wear masks to wear them, and convince political and religious leaders to remind people of the importance of wearing masks. In this way, the scientists not only managed to substantially increase the use of masks among the selected populations (from 13.3% to 42.3%), but this use was maintained over time.
The researchers also observed that the protective effect of the masks was much more marked among people older than 60 years, with a decrease of infected people, with symptoms and positive for antibodies, of 34.7%
Researchers surveyed trial participants periodically (at five and nine weeks after the start of the study) to find out if they had typical COVID-19 symptoms, and then at 10 and 12 weeks they performed blood tests (serological ) to those who accepted to see if they had developed antibodies against SARS-CoV-2.
In the villages where the use of masks was promoted, with an increase of almost 30% in their use, a reduction in the relative risk of suffering an infection with symptoms due to the coronavirus with confirmed antibodies in blood was observed. In the control group, 8.6% of people reporting infections with COVID-19 symptoms and antibodies were detected, compared with 7.6% of people in the group where the use of masks was promoted. However, the observed effect was very different depending on the type of mask being promoted. While the COVID-19 reduction effect was significant for surgical masks (11.2% risk reduction), it was much smaller and not significant for cloth masks (5% risk reduction). The weighted data represent, according to the authors, a 9.3% decrease in risk.
The researchers also observed that the protective effect of the masks was much more marked among people over 60 years of age, with a decrease of those infected by coronavirus, with symptoms and positive for antibodies, of 34.7%. This finding could be due to the fact that older people tend to show symptoms more frequently and, therefore, the study detected the coronavirus infection more rigorously in them than in young people, where it often goes unnoticed.
Ultimately, this study shows that promoting the use of masks in the general population, through actions with proven efficacy, can be a safe and cheap measure to limit, to some extent, coronavirus infections in the community.
Although this study is, for now, the best when it comes to assessing the decrease in symptomatic coronavirus infections thanks to the increase in the use of masks in the general population (in the real world), it still has important limitations . First of all, the cultural factor should not be neglected. Actions that have been shown to promote the use of masks in Bangladesh may have a different effect in other countries. Another detail that limits knowing the true value of the masks to stop the infections by SARS-CoV-2 is that they did not make an active detection of asymptomatic infections, so they were off the “radar” of the researchers. As a consequence, this could underestimate the actual effect of the masks.
Another important limitation of the trial is that the researchers observed that in the villages where the actions to promote the masks were carried out, the inhabitants also complied more with the safety distance. This, again, makes it difficult to know the true magnitude of the effect of the masks. In any case, the study authors intend to continue their research to delve further into the role of masks in preventing coronavirus infections.
Beyond its limitations (which all scientific studies possess to a greater or lesser extent), this research is, to date, the best proof of the value of masks in the real world to prevent symptomatic infections by the new coronavirus. Finding out the true magnitude of the effect of masks against epidemics is a real challenge and this gigantic study sheds some light on this. The effects of masks would probably be much more evident if, instead of moderately increasing the use of masks in the general population, the correct and universal use of these protective elements were established.