Are masks useful for Covid and other illnesses? Understand – 03/14/2023 – Balance and Health
The publication of research on the use of a mask to stop respiratory infections, as in the case of Covid-19, raised doubts about its effectiveness. For the authors of the analysis, it is not possible to fully conclude that it reduces the spread of viruses.
The point clashes with other evidence that indicates the effectiveness and importance of using a mask to stop the transmission of Sars-CoV-2. In addition to creating a barrier that prevents the inhalation of potentially viral particles, it prevents someone who is sick from spreading the virus.
The research that sparked the discussion was published by the Cochrane Library, an initiative that analyzes scientific evidence to guide the adoption of public health measures.
The study was initially published in 2007 and has been updated over the years – this is the fifth version and for the first time presents data from Covid-19.
The publication is what is called a systematic review. This type of methodology focuses on information from previously published research, listing the degree of confidence of this evidence.
In the case of surgical masks, the researchers explored 12 articles. In nine of them, carried out in different social contexts and with more than 270,000 people, the authors did not observe a significant advantage of the piece in preventing respiratory infections similar to Covid, such as the flu.
For the N95 type, the number of searches compiled in the review was five. In addition to not identifying a clear benefit of using them compared to surgical ones, the review pointed out that N95s do not seem to play a central role against respiratory diseases: in three of the studies analyzed, with a total sum of 7,000 participants, the item did not present an advantage for stop infections.
The variety between these studies is an aspect that calls the attention of Vitor Mori, a researcher at the University of Vermont, in the USA, and member of the Observatório Covid-19 BR initiative. He states that, as it is a systematic review, the publication compiled studies with different characteristics without considering the specificities of each one of them.
“When you do that, you take away some of the nuance and impact of each work”, says the researcher, who does not subscribe to the Cochrane Library review.
The results are also not necessarily a final indication that masks don’t work. There is evidence in favor of the equipment already published in other studies, such as a Brazilian one that evaluated 227 models of the piece. Aerosol particles smaller than those of Sars-CoV-2 were emitted and it was then possible to measure the filtering of the masks —the PFF2/N95 type achieved the best result, between 90% and 98%.
Furthermore, a systematic review may conclude that there is not enough information, nor with a high degree of confidence, to arrive at a correct answer around the question that guides the research. This is the case of the Cochrane Library review.
In the publication, the scientists point out that it is not known whether the use of surgical or N95-type masks “help to delay the spread of respiratory viruses based on the studies we have carried out”, but add that “the results may change when more evidence is available “.
An example that the conclusion of the study is subject to change are the previous versions of the review. The one made in 2020, for example, indicates a lack of confidence in the effectiveness of the mask. However, other versions of the survey concluded that it could be a useful measure against respiratory infections.
“The implementation of transmission barriers, such as isolation and hygiene measures (use of masks, gloves and aprons), can be effective in containing respiratory virus epidemics”, the authors wrote in the version published in 2011.
For the most recent review, the scientists who signed the survey noted some causes to explain the inaccuracy of the research findings.
One of them is the low adherence of people to the use of masks. That is, even composing the sample for a study on the effectiveness of the equipment, many did not adhere consistently and correctly to it. According to the authors, this aspect “may have affected the results of the studies”.
This factor is also reported by Erick Sousa, researcher at ITPS (Instituto Todos Pela Saúde). He explains that the review looked at randomized clinical trials. In these studies, the intervention that is investigated –a medicine, for example– must not vary between participants in order to arrive at an exact result. That is, the people participating in the trial need to have similar access and be exposed to circumstances close to those that the study investigates so that, in the end, the effects of the intervention are reliable.
But using this same methodology in the case of masks can lead to problems. It is difficult, for example, to standardize the use of equipment among all participants. The review authors themselves explored this aspect by noting that many study participants did not use the protective garment in a similar way.
It is also complex to standardize the exposure that these people would have to viral particles – some may have more, while others, less. “When choosing individuals to carry out the study, I cannot guarantee that the exposure of the intervention is equal”, says Sousa, who was not involved in the review.
According to him, if clinical trials had better standardization of exposure to respiratory particles and also a similar intervention of mask use, the results could be more accurate.
A Sheet tried to contact the authors, but they did not respond.
For Mori, updating the Cochrane Library material may, above all, be an indication of the need to think about how to create interventions and public policies with this equipment so that its benefits are better used.
“Perhaps the conclusion that we can draw from this study is that, if you don’t have ideal adherence to mask use, if you don’t have more focused policies, if you simply tell people ‘wear a mask’ without going into detail about where this is most necessary, which type of mask is better, how to use it correctly, you can lose potential [do equipamento] to avoid and reduce the transmission”, says Mori.