Washington (AFP)
Many passers-by or cyclists travel through major American cities wearing a mask, even when they are far from each other.
Some American states, such as Maine, also continue to require the wearing of masks on hiking trails and beaches.
The question of the usefulness of such measures is debated by experts.
- It is much safer to be outside
Scientists have learned a lot about Covid-19 since the start of the pandemic.
They now know that surfaces do not play a big role in the transmission of the virus and that excessive disinfection is a waste of time and resources.
However, many experts consider the transmission of the disease to be aerial.
It is mainly spread via fine particles that stay suspended in the air for a certain period of time, and not by droplets emitted by a cough or sneeze, which quickly fall to the ground.
That's why it's much safer to be outdoors than indoors, says Jose-Luis Jimenez, an aerosol expert and professor at the University of Colorado Boulder.
"It is much more dangerous to be inside because the walls, the ceiling and the floor trap the air", especially in case of poor ventilation, he told AFP.
"The outside is much less risky because there is more air in movement" and the air we breathe out rises, especially when it is hot. Protective masks against the coronavirus
- What are the risks of infection?
There are now several studies on the risks of contamination outside.
Last October, Chinese researchers published an investigation in the journal Indoor Air, in which they compiled information on 7,324 cases, including the location where the virus had been transmitted.
Of the more than 7,000 cases, only one concerned transmission outside: a 27-year-old villager infected in January 2020 after a conversation outside with an infected person, near Shangqiu, in central Henan province.
More recently, the Irish Times newspaper asked Irish health authorities how many of the 232,164 cases in the country as of March 24, 2021 had been infected outside.
The response was 262 cases, or just 0.1% of the total.
This estimate may be overstated, given that authorities relied on unverified information from outside activities - such as a construction job or playing a sport - but some people concerned may have also been able to rely on it. participating in rallies inside.
Donald Milton, a professor at the University of Maryland and one of the pioneers of aerosol science, advises avoiding crowds outside, especially when shouting or singing like at a game is planned, a concert or an event, and if there is no wind.
But he doesn't think wearing a mask all the time outdoors is necessary.
"When I jog in my neighborhood, where houses are spaced at least 10 meters apart and there are only a few people walking their dogs and children playing in gardens, I keep my mask in. my pocket, "he says.
“I can't run for very long with my mask on,” he explains.
"If I stop to talk to people, I can put it on. If I walk with friends, I wear it."
- The politicized mask
Wearing a mask has become a highly politicized issue in the United States, where the conservatives, under the leadership of Donald Trump, see it as an affront to their individual freedom.
Progressives generally take the virus more seriously and see the mask as a way to show solidarity with their neighbor in times of crisis.
But for Amesh Adalja, a public health expert at Johns Hopkins University, it's time to reverse the requirement to wear a mask outdoors and take a more nuanced, science-based approach.
"The masks have been so politicized that some people denounce other individuals to shame them," he regrets.
"I think it's counterproductive."
"What we want is that people, and especially those who are not vaccinated, to wear a mask when they are indoors and that they cannot respect social distancing", explains the expert. .
Giving the impression that it is dangerous to be outside could cause people to gather indoors, which is worse, he says.
Some experts argue that the advantage of making the wearing of a mask mandatory outside is that it simplifies the message to the public, to which Amesh Adalja objects.
"The only result is that the public has less confidence in health authorities," he said, noting that the public is able to read medical journals and realize that public discourse differs from scientific data. .
© 2021 AFP