Having told their populations that wearing masks was all but useless against the coronavirus, several Western countries have performed dramatic U-turns in the last few days.
The rapid rethink as the number of deaths has rocketed has stirred anger and confusion, with some accusing their leaders of lying to them.
The most spectacular about-turn has been in the United States where President Donald Trump on Friday urged all Americans to wear a mask when they leave home.
With America accused of gazumping and even "piracy" by Berlin to procure masks, Trump later said he would probably not wear one himself -- although his wife Melania tweeted that everyone should.
While mask wearing has been widespread in Asia since the beginning of the epidemic, the World Health Organization (WHO) and numerous governments have insisted that they should only be worn by carers.
This stance was seen as way to protect the dwindling stocks of surgical and FFP2 masks -- which offer the most protection.
Seen from Asia, where wearing masks during the flu season is normal, Western reluctance seemed utterly baffling.
There is a "definite shift in the position of the US" towards wearing masks, Professor K.K. Cheng, a public health specialist at Birmingham University in Britain, told AFP.
The expert, a strong advocate of their use, said the WHO was reviewing its guidance.
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"The big mistake in the US and Europe is that people aren't wearing masks," George Gao, the head of the China Centre for Disease Control, told the journal Science.
Experts agree that surgical masks are not a foolproof way to prevent coronavirus infection.
But people infected with the virus are advised to wear them to stop the spread to others, with evidence that transmission can happen before a person knows they are sick.
Another argument in their favour is the theory -- not yet scientifically proven -- that the virus can be transmitted through the air.
'Spread through speaking'
Dr Anthony Fauci, who is leading the US government's response, has backed research that found it can be suspended in ultrafine mist formed when people exhale.
Research indicates "the virus can actually be spread even when people just speak as opposed to coughing and sneezing," Fauci told Fox News.
If that is confirmed, it would explain why the virus so contagious.
Even before the White House recommended masks, Bill de Blasio, the mayor of New York, which has been badly hit by the epidemic, said residents should cover their faces when they got out.
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"That could be a scarf or something you make yourself, a bandana," he said.
Germany's disease control agency, the Robert Koch Institute, also urged Germans to wear homemade masks as many people across Europe and North America turned to online DIY tutorials posted by medical experts.
Koch Institute head Lothar Wieler said masks "could help to protect others, but they don't help protect the wearer themselves.
"That is very important to understand," he added, a message repeated by Professor Cheng.
'Better than nothing'
"You wear a mask to reduce droplets from one's own respiratory tract. It only works if everyone wears them, and if everyone does, you only need a very basic mask.
"A piece of tissue can block it. It's not perfect, but it's much better than nothing," he said.
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In another major shift Friday, the French Academy of Medicine said that masks should be made obligatory for everyone leaving their homes during the lockdown.
Its recommendation came after much online anger when television presenter Marina Carrere d'Encausse, herself a doctor, said that the French government line that masks we only useful for carers was a "lie (told) for a good cause".
The country's response to the epidemic has, like many others, been dogged by reports of shortages of masks and other protective equipment for nurses and doctors.
Masks are already compulsory in the Czech Republic and Slovenia and anyone going into a supermarket or food store in Austria has to wear one.
Masks can 'reduce' virus
The WHO, however, is sticking by its initial advice, fearful that masks could give the public "a false sense of security" that would lead to people being more casual about social distancing and hand washing.
But its head Dr Tedros Adhanom Ghebreyesus conceded Wednesday that there "is an ongoing debate about the use of masks at community level".
"This is still a very new virus and we're learning all the time. As the pandemic evolves, so does the evidence and so does our advice," he added.
A study that appeared Friday in the review Nature will give the WHO plenty to think about, however.
It concluded that masks reduce the quantity of coronavirus breathed out into the air by people carrying it. The research was done with other members of the coronavirus family rather than the SARS-CoV-2 strain responsible for the current pandemic.
"This new study presents strong and compelling evidence in favour of mask wearing," said infection expert Dr Rupert Beale of the Francis Crick Institute in London.
"Public health officials must immediately take note of this important new evidence. Mask wearing does not completely prevent transmission... but (it) should form part of the 'exit strategy' from lockdown," he added.