Wearing a mask outdoors and putting it in a pocket when entering a bar is like wearing a helmet when walking and taking it off when getting on a motorbike. Despite this, it is common to see this paradox in many countries like Spain, where it is mandatory to wear a mask when going out, but there are exceptions for indoor spaces such as restaurants and offices. But a growing number of leading experts are beginning to question these contradictory measures, including Marc Lipsitch, head of the Center for Infectious Disease Dynamics at Harvard University, USA. “I am generally someone who likes to uphold the rules with clear interests. Outdoor masking has significant costs and really no evidence of benefit,” he wrote on Monday in a message on Twitter.

There has been substantial data on the spread of coronavirus for a year now. A study of 318 coronavirus outbreaks in China, conducted at the beginning of the pandemic, found that 317 outbreaks were in indoor spaces. Only one of the 318 outbreaks occurred outdoors as a 27-year-old man who presumably contracted the coronavirus in a town was talking outside with a newcomer from Wuhan, where the virus first emerged. first is determined. The European Center for Disease Prevention and Control (ECDC) only recommends that masks should be worn in confined spaces, but “may be considered in crowded outdoor environments”. However, in Spain, masks are mandatory even when a person is walking in a park. Under current regulations, masks must be worn in all public spaces, regardless of whether social distancing is respected or not. On April 6, the Madrid Association of Public Health (Amasap) called for an end to the “absurd” mandatory use of face masks in outdoor spaces.

According to new research published last week in the medical journal, the coronavirus is mainly spread through the air, via aerosols, which accumulate like an invisible cloud when a person talks or coughs. Fingertips. The study’s authors – led by Dr Trish Greenhalgh from the University of Oxford in the UK – say the way to prevent the disease from spreading is: avoid being indoors with people from another household, increase communication wind, use a well-fitted mask in indoor spaces and reduce capacity.

“We only need to wear a mask when we are doing strenuous exercise, such as running if we are passing very close to someone, on the sidewalk,” Greenhalgh said. “For everything else, it is not necessary to wear a mask when outdoors, as the virus quickly dissipates in the air. But if I breathe in the air you just exhaled, I’m at risk.”

Chemical engineer Martin Bazant, who creates an interactive tool that calculates the risk of infection, says airborne transmission of the virus in enclosed spaces is the main cause of the pandemic’s spread. There’s a particular dynamic to coronavirus, where some positive cases become super-spreaders, while others don’t even spread to someone they share a bed with at night. Bazant points out that all of the reported cases of mass transmission have taken place indoors, such as the outbreak of 53 cases in a church choir in Mount Vernon, or 23 people infected across the country. a bus ride in Ningbo, China. In these enclosed and poorly ventilated spaces, wearing a mask is very important.

The possibility of disease transmission outdoors is at least 20 times lower than indoors

Open letter from Spanish medical professionals

Bazant, who works at the Massachusetts Institute of Technology, explains that “outdoor transmission is extremely rare, even at the start of the pandemic, when no one was wearing a mask.” The engineer explains that when outdoors, the air exhaled from the mouth tends to be warmer than the surroundings, which means it quickly rises up and is blown away by the air currents. “A spread can only be expected when people are very close to each other, a meter or less, and talk face to face, as happened in China in the only recorded case of outdoor transmission. And even then, the risk is much lower than in indoor spaces,” says Bazant, who adds, “it’s time to stop using masks outdoors.”

US health authorities require the use of masks when indoors and on public transport, but say they “may not be necessary when you are out alone, away from other people or with people living in your household”. The World Health Organization (WHO) only recommends the use of masks when it is not possible to maintain a safe distance of one meter.

Over the past year, researcher Lidia Morawska has led a scientific movement to convince the world’s main health authorities of the importance of airborne transmission for the spread of coronavirus. Like other leading scientists, Morawska also firmly believes that masks are not always needed when outdoors. “I always say that outdoors, when one is moving and can maintain a reasonable distance, a mask is not necessary,” she explains. “For example, walk in the park, jog, ride a bike. However, we need masks outdoors if we are in a crowd or very close to other people.”

People wearing face masks in the Catalan city of Cubelles.CRISTÓBAL CASTRO

An international team of scientists published in January an assessment of the role of masks in the fight against the coronavirus. At the time, the authors suggested that “the widespread use of masks in public places” had reduced transmission of the virus. But the study’s first author, Jeremy Howard, a data scientist from the University of San Francisco, now says it’s “generally not necessary to wear a mask outdoors,” as long as it’s windy and the person is walk or run.

Helene-Mari Van Der Westhuizen, one of the co-authors of the January study, also believes there’s no need to wear a mask when walking in public places, but argues that there are risks depending on the situation. situation. “If I go to an open-air market crowded with people, if I run past someone in a narrow street or if I am walking with my grandmother who has not been vaccinated, then yes, obviously I will put “masks,” said the researcher from the University of Oxford, who urged health authorities to include these nuances in their recommendations. “It is much safer to be outdoors than indoors, but you must continue to use a mask if you cannot maintain a safe distance or if you are coming into contact with someone in a high-risk group. severe cases of Covid,” she said.

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More than 100 Spanish experts signed an open letter on March 25 calling on the authorities to “reconsider the recommendations on prevention”, arguing that “the possibility of infection outdoors is less than 20 times more than indoors”. One of the scientists who signed the letter, chemist José Luis Jiménez, from the University of Colorado, explained that the letter avoids saying that masks are unnecessary when outdoors and social distancing, because Some public health experts fear the message could be misinterpreted as face masks. never needed.

A spokesman for Spain’s Health Ministry said for now “all security measures will continue to be maintained” – including the mandatory use of masks in public spaces, regardless of society. far. A medical expert argues that it is better not to risk changing the rules until more people are vaccinated against Covid-19. In Israel, for example, this week the government announced that masks no longer need to be worn outdoors, but only after more than half of the population has been vaccinated. In Spain, 21% of the population has received at least one dose of the Covid-19 vaccine, but only 7.6% have received the two shots needed for full protection from Oxford-AstraZeneca, Moderna and Pfizer-BioNTech provide.

English version by Melissa Kitson.

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