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Without vaccines or effective treatments in the nearest horizon, protection, hygiene and social distance measures are the best way to prevent SARS-CoV-2 infection. This is confirmed by new research that, for the first time, has made a systematic review of the most effective interventions to reduce the risk of infection. According to his data, two meters of separation in front of other people is better than one; the mask must be an essential tool and eye protection could provide, to a lesser extent, an additional benefit. 

"Our data provides the best evidence currently available on the optimal use of these three simple and common interventions," said Holger Schünemann, a researcher at McMaster University in Canada and one of the people responsible for the meta-analysis just published in a statement. scientific journal The Lancet.

In any case, the authors stress in the work - which has taken into account the results of 172 observational studies from 16 countries - that none of these measures - even when used in combination and appropriately - guarantees total protection against the virus .

Since the new coronavirus came into our lives, there have been conflicting recommendations on how best to protect yourself against its effects (wearing masks is perhaps the most palpable example). So Schünemann's team wanted to analyze the scientific data available so far to get a clear picture of the situation. However, despite the large amount of data they have handled, the available evidence on the effectiveness of some measures, such as eye protection, remains low, they acknowledge. 

Finally, 44 studies were included in the work, with data from 25,697 patients affected by Covid-19 or its 'close relatives', the SARS and MERS coronaviruses. .

Analyzing the evidence on the impact of social distance on virus transmission, the researchers found that maintaining at least a meter of separation from other people significantly reduces the risk of infection. However, this possibility is minimized much more if they are maintained at least two meters away. Thus, the risk of infection goes from being around 13% if people are less than a meter away, to being 2.6% if this distance is respected. With one more meter of separation, they point out, the protection is multiplied by two (1.3%). 

For Ildefonso Hernández, professor of Public Health at the Miguel Hernández University of Alicante, the results of this work confirm not only that "the physical distance very clearly reduces the risk", but also that two meters can be an acceptable measure for identifying the possible contacts of a positive case. "The limit of the two meters of people who have been in contact with an index case is correct," he maintains. 

The work has also reviewed the available data on the usefulness of eye protection. According to their analyzes, this measure - for example, the use of screens or glasses - can also be a useful tool against the virus (the risk of infection goes from 16% to 5.5%). In any case, as in the case of masks, the researchers acknowledge that, in this field, the evidence that there is so far is low, so they demand new research in this regard.   

Regarding the effectiveness of the masks, the researchers also certified their usefulness. Without this protection, the risk of virus transmission is 17.4%. With it, it drops to 3.1%, they point out. Based on their data, FFP2 or equivalent masks are more effective than surgical or reusable ones. However, given the lack of availability in many contexts of the most efficient filtering masks, such as FFP2, their use should be prioritized in healthcare facilities. 

Angel Asensio, head of the Preventive Medicine service at the Puerta de Hierro University Hospital in Majadahonda (Madrid), agrees with his point of view. "The use of FFP2 for the population could be theoretically effective, but in practice breathing through these masks wearing them tight enough, which is how they are effective, is very uncomfortable because it makes breathing difficult, especially in older people or sick or if they are doing some physical exercise, among other reasons, "he points out. In addition, he adds, "while there is a shortage of these masks, which last for hours, they should be prioritized for professionals , who are the most exposed to aerosols from the patients they serve." 

The use of surgical masks among the general population should be mandatory in closed environments and if the safety distance cannot be maintained, Asensio continues, "not only because they can protect us from the virus reaching us" but, above all, "because they control to the emitting focus. If a person is infected and has a mask, it is very unlikely that they can send viruses abroad, "he stresses.  

In this sense, the research indicates that reusable multi-layer masks are much more effective than those with only one layer, an aspect to take into account when making homemade or fabric masks.

The data, adds Hernández for his part, "provide enough evidence to defend the community use of masks." Therefore, "it will be necessary for us to continue using them in our social relationships and in places where physical distance cannot be maintained," adds the specialist, who suggests that the recommendation of eye protection could be considered "particularly in people at higher risk "

Ángel Asensio points out that eye protection would not be necessary in the general population but, on the other hand, it is essential to highlight the importance of hand hygiene when it comes to preventing infections. "It is a key measure," he remarks.

In the research published in The Lancet , the scientists conclude by stressing that health authorities should take these conclusions into account when developing protection policies against the virus.

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