Face visors may not stop infected patients spreading coronavirus, a leading public health expert has warned.
Britons are now being encouraged to wear face masks on public transport and in situations where social distancing is not achievable, such as in shops.
Retailers such as Marks & Spencer and Waitrose have even bought transparent visors for staff to wear in a bid to protect them against COVID-19.
But Professor Linda Bauld, of the University of Edinburgh said the visor may not prevent people from spreading the virus to other people.
While masks are thought to have the opposite benefit – preventing spread but not necessarily infection – Professor Bauld said visors are unlikely to do a good enough job of containing breath droplets exhaled by the wearer.
Face visors are being worn around the world by people trying to protect themselves from the coronavirus, but experts are sceptical that they can stop someone spreading the virus if worn without a mask (Pictured: A security guard in Belgium wearing a visor)
‘I don’t think there’s any strong evidence they’re something the public should be wearing on a routine basis,’ Professor Bauld told The Guardian.
‘The key thing is to cover the mouth and the nose.
‘The face coverings that people are being encouraged to use, for example, on public transport is not to protect the wearer, but to protect other people.’
Professor Linda Bauld, from the University of Edinburgh, told The Guardian: ‘I don’t think there’s any strong evidence they’re something the public should be wearing on a routine basis’
In comparison to face masks, the visor would be intended to stop droplets from breath, coughs or sneezes drifting into the wearer’s face, but would be unlikely to stop air coming out of their own nose and mouth.
Masks are such a hot topic because of the way the coronavirus spreads – it infects people by piggy-backing on droplets of moisture which are expelled from people’s lungs when they breathe.
These go further if someone coughs or sneezes and, if they’re inhaled by someone else, the viruses can latch onto cells in the airways and trigger COVID-19.
Explaining the one-sided benefit of a visor, Professor Bauld added: ‘The reason for having a visor which would cover the upper half of your face would be if you’re regularly coming into contact with the public at closer range, and you might be exposed to somebody who is emitting those small droplets that we’re all aware are very efficient at carrying the virus.’
Professor Bauld’s comments come after doctors at the University of Iowa last month claimed face shields ‘offer a number of advantages’ in fighting the pandemic.
In an article published in the Journal of the American Medical Association (JAMA), they said: ‘Face shields can be reused indefinitely and are easily cleaned with soap and water, or common household disinfectants.
‘They are comfortable to wear, protect the portals of viral entry, and reduce the potential for auto-inoculation by preventing the wearer from touching their face.’
‘People wearing medical masks often have to remove them to communicate with others around them; this is not necessary with face shields.
‘The use of a face shield is also a reminder to maintain social distancing, but allows visibility of facial expressions and lip movements for speech perception.’
The piece, authored by Iowa’s Dr Eli Perencevich, said that shields ‘appear to significantly reduce the amount of virus’ inhaled.
THE TRUTH ABOUT FACE MASKS: WHAT STUDIES HAVE SHOWN
Research on how well various types of masks and face coverings varies but, recently, and in light of the pandemic of COVID-19, experts are increasingly leaning toward the notion that something is better than nothing.
A University of Oxford study published on March 30 concluded that surgical masks are just as effective at preventing respiratory infections as N95 masks for doctors, nurses and other health care workers.
It’s too early for their to be reliable data on how well they prevent infection with COVID-19, but the study found the thinner, cheaper masks do work in flu outbreaks.
The difference between surgical or face masks and N95 masks lies in the size of particles that can – and more importantly, can’t – get though the materials.
N95 respirators are made of thick, tightly woven and molded material that fits tightly over the face and can stop 95 percent of all airborne particles, while surgical masks are thinner, fit more loosely, and more porous.
This makes surgical masks much more comfortable to breathe and work in, but less effective at stopping small particles from entering your mouth and nose.
Droplets of saliva and mucous from coughs and sneezes are very small, and viral particles themselves are particularly tiny – in fact, they’re about 20-times smaller than bacteria.
For this reason, a JAMA study published this month still contended that people without symptoms should not wear surgical masks, because there is not proof the gear will protect them from infection – although they may keep people who are coughing and sneezing from infecting others.
But the Oxford analysis of past studies- which has not yet been peer reviewed – found that surgical masks were worth wearing and didn’t provide statistically less protection than N95 for health care workers around flu patients.
However, any face mask is only as good as other health and hygiene practices. Experts universally agree that there’s simply no replacement for thorough, frequent hand-washing for preventing disease transmission.
Some think the masks may also help to ‘train’ people not to touch their faces, while others argue that the unfamiliar garment will just make people do it more, actually raising infection risks.
If the CDC does instruct Americans to wear masks, it could create a second issue: Hospitals already face shortages of masks and other PPE.
Some research has shown that people are at risk of becoming more seriously ill with COVID-19 if they receive a larger ‘viral load’ – the first dose of viruses that they are infected with.
Dr Perencevich and colleagues pointed to a study that simulated how much of a flu virus a healthcare worker wearing a visor would have been exposed to.
Results showed they inhaled around 92 per cent less of the virus when standing 2m away – the strict social distancing advice.
But the same study revealed shields were less effective after 30 minutes, when the particles had dispersed into the surrounding room.
Dr Perencevich and colleagues added that ‘major policy recommendations should be evaluated using clinical studies’.
But they said: ‘It is unlikely a randomized trial of face shields could be completed in time to verify efficacy.
‘No clinical trial has been conducted to assess the efficacy of widespread testing and contact tracing, but that approach is based on years of experience.
‘Face shields… should be included as part of strategies to safely and significantly reduce transmission in the community setting.’
Tech giant Apple last month announced it was going to begin producing its own face shields for medical workers battling the pandemic.
Chief executive Tim Cook said it had also designed its own transparent protective visor and begun mass production at its factories in the US and China.
Last week Apple revealed it plans to sell them to the public soon and that it would sell shields at cost, meaning it won’t make a profit off of them.
British chocolate giant Cadbury has also started to make visors, teaming up with engineering firm 3P Innovation to produce thousands of the gadgets.
The visors will be made through 3D printing technology, which is normally used to make chocolate sculptures at the chocolatier’s factory in Bournville.
Frontline NHS workers, including nurses treating coronavirus patients in intensive care, are told to wear visors.
Medics are also instructed to wear shields during aerosol-generating procedures, such as intubating a patient.
If in ‘extremely short supply’, medics are urged to re-use single-use visors. They must cover the forehead, extend below the chin and wrap around the face.
They should be cleaned using a detergent – the same decontamination process used for any bit of PPE that needs to be donned again.
Visors will degrade with repeated cleaning, according to the guidance, which says they should be ‘resupplied regularly’.
Waitrose announced it had ordered protective visors at the end of March, revealing staff could wear them at work if they wanted to stay safe.
Marks and Spencer followed suit weeks later and gave front-line employees plastic face shields, to protect them against COVID-19.
And Co-op introduced visors earlier this month, giving thousands of staff the option to wear the gadgets during their shift if they wanted.
It comes after a study last week found men are less likely to wear face masks than women because they are seen as ‘not cool’ and ‘a sign of weakness’.
Experts surveyed nearly 2,500 US adults, finding that men were more likely to see face masks as being ‘shameful’ and be put off by the perceived stigma.
Eight per cent of men and five per cent of women said they would definitely not be wearing a face mask when outside of their homes.