Should more of us wear face masks to help slow the spread of coronavirus?
This question is to be assessed by a panel of advisers to the World Health Organization (WHO).
The group will weigh up research on whether the virus can be projected further than previously thought; a study in the US suggests coughs can reach 6m and sneezes up to 8m.
The panel’s chair, Prof David Heymann, told BBC News that the new research may lead to a shift in advice about masks.
The former director at the WHO explained: “The WHO is opening up its discussion again looking at the new evidence to see whether or not there should be a change in the way it’s recommending masks should be used.”
What is the current advice?
The WHO recommends keeping a distance of at least 1m from anyone coughing or sneezing to avoid the risk of infection.
It says people who are sick and show symptoms should wear masks.
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But it advises that healthy people only need to wear them if they are caring for others suspected of being infected or if they themselves are coughing or sneezing.
It emphasises that masks are only effective if combined with frequent hand-washing and used and disposed of properly.
The UK, along with other countries including the US, advises that social distancing should mean staying at least 2m apart.
This advice is based on evidence showing that viruses can only be transmitted while carried within drops of liquid.
The understanding is that most of those drops will either evaporate or fall to the ground near to the person who released them.
So what does the new research say?
Researchers at the Massachusetts Institute of Technology (MIT) in Cambridge, US, used high-speed cameras and other sensors to assess precisely what happens after a cough or sneeze.
They found that an exhalation generates a small fast-moving cloud of gas that can contain droplets of liquid of varying sizes – and that the smallest of these can be carried in the cloud over long distances.
The study – conducted in laboratory conditions – found that coughs can project liquid up to 6m away and that sneezes, which involve much higher speeds, can reach up to 8m away.
What are the implications?
The scientist who led the study, Prof Lydia Bourouiba of MIT, told me that she is concerned about the current concept of “safe distances”.
“What we exhale, cough or sneeze is a gas cloud that has high momentum that can go far, traps the drops of all sizes in it and carries them through the room,” she said.
“So having this false idea of safety at one to two metres, that somehow drops will just fall to the ground at that distance is not based on what we have quantified, measured and visualised directly.”
Does this change the advice about masks?
Prof Bourouiba’s view is that in certain situations, especially indoors in poorly ventilated rooms, wearing masks would reduce the risks.
For example, when facing someone who’s infected, masks could help divert the flow of their breath and its load of virus away from your mouth.
“Flimsy masks are not going to protect from inhaling the smallest particulates in the air because they do not provide filtration,” Prof Bourouiba said.
“But they would potentially divert the cloud that is being emitted with high momentum to the side instead of forward.”