Face coverings “can be useful” in some outdoor environments in helping to stop the spread of COVID-19, a top medical expert has said.

At the moment, masks are not required to be worn outside when in public, but Welsh health minister Vaughan Gething and London mayor Sadiq Khan have recently urged people to wear them when leaving the house.

Researchers now know that COVID-19 is airborne and can be spread from the breath of those who are infected, but it is not clear what proportion of transmission this actually accounts or how long it takes for it to be transmitted when in someone else’s presence.

Speaking about face masks on Sky News, the UK’s chief scientific adviser Sir Patrick Vallance said: “They can be useful in outdoor environments where there’s crowding but frankly there shouldn’t be crowding.

“They are probably of no value where you are outside generally or just passing somebody for a second but they may have a role in other environments.

“One might think of somewhere like an outdoor market where someone should wear face coverings but I should say the really key thing is avoid crowding.

“What I think is clear is that face masks are most effective at preventing spread from the person wearing them. So they’re useful to stop people who might not know they have the disease who maybe are of course asymptomatic because you shouldn’t be out and about anyway if you’ve got the symptoms but asymptomatic people from spreading from releasing it towards others. That’s where they’re most effective.”

But his mask and face covering comments are not in agreement with Downing Street’s deputy chief medical officer, who last week said they only ned to be worn inside.

Professor Jonathan Van-Tam said: “My view remains that the really high-risk environments for transmissions are indoor spaces, and the Government advice is to wear masks, face coverings, in indoor spaces.”

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