April 22, 2020

expert comment on use of facemasks in public settings

There has been continued discussion in the media about the use of facemasks in public settings to help counter the spread of COVID-19.

Prof Sian Griffiths, Emeritus Professor, the Chinese University of Hong Kong, and co-chair of the Hong Kong government’s SARS inquiry, said:

“The question of masks has been discussed by SAGE and advice is being formulated to give to ministers who will review and if necessary, update current policy. Increased use of masks risks diversion away from those who are in clinical need – patients, health care workers and care home staff. Meanwhile, many other countries are seeing mask wearing as part of the approach to reducing community transmission post -lockdown. The scientific debate on effectiveness is between different approaches to assessing how effective masks are at stopping infection, particularly in community settings. However full or partial use of masks will be part of lockdown deceleration in most European countries, not just Asian countries where mask wearing for infections is already part of the culture in the post SARS world. In the US, to avoid shortage of masks in situations where they are clinically needed ,the CDC has recommended cloth face coverings as part of the drive to reduce transmission of the virus and even provided patterns so they can be home made. In the UK we await further update from ministers when they have reviewed the latest evidence.”

Prof KK Cheng, Director, Institute of Applied Health Research, University of Birmingham, said:

“To wear a mask or not in the community is one of the most debated issues in the Covid-19 pandemic. It is yet to be recommended by either the World Health Organisation (WHO) and Public Health England (PHE) but most other high-income countries now require or recommend that their citizens wear face masks in public. Since early March, some of the academic community, including myself have argued in The Lancet and the BMJ that it’s time for the UK to do the same.

“The main reason behind the advice of PHE and the WHO is that there is no evidence that mass use of masks is effective in preventing SARS-CoV-2 infection. Most people wear masks to protect themselves. However, because of possible transmission of this disease by those who are asymptomatic, a stronger reason for wearing masks is that it would act as a form of source control and will protect others from respiratory droplets emitting from one’s airway. The WHO and PHE have erroneously equated absence of evidence of effectiveness from clinical trials on mass masking to evidence of ineffectiveness.

“In fact, there are strong mechanistic reasons for covering the mouth to reduce respiratory droplet transmission. If it does not work, why do we ask people to cover their mouths when coughing or sneezing. But the faith on respiratory etiquette is not based on clinical trials. In view of the global shortage of masks, medical masks must be reserved for health-care workers. Thankfully, to control the infection source rather than to self-protect, cloth masks are likely to be adequate, especially if everyone wears a mask.  In the current lockdown, social distancing is of prime importance. But when shopping at supermarkets or when essential workers travel to work in public transport, mask wearing would be useful in reducing the risk for everyone. As we consider the strategy of exit from lockdown, mass masking could be an important public health measure that would help alleviating the risk arising from the relaxation of social distancing.”

Prof William Keevil, Professor of Environmental Healthcare, University of Southampton, said:

“There is a lot of pressure from some governments around the world and some of the public to wear face masks, if only to feel empowered that they can contribute practically to returning to a more normal life without becoming infected. The majority of home-made masks such as scarves and folded T-shirts do not filter well although, interestingly, a new unrefereed study by Cleanair suggests thick canvas, denim and kitchen towels are quite good filters but these were static tests and not fitted to the face. Gaps between the face and ill-fitting masks make it easy for contaminated air to bypass the masks. In general, better filtration materials, if fitted properly, make breathing more difficult.

“People should ask – why am I wearing a mask? Is it to protect me – in which case only FFP2 and FFP3 masks are rated for this, as worn by front line ICU staff and emergency responders who breach the 2-metre gap; the many poor quality, loose fitting “surgical” face masks commonly available on the internet do not offer this personal protection. Alternatively, is it to protect others – in this case a mask can catch very large airborne respiratory droplets produced from breathing or coughing (making the mask surface wet, such that the mask should be rated for wettability performance otherwise virus penetration increases across a wet mask) while smaller respiratory droplets and very small aerosol particles will be diverted from a frontal direction which may otherwise travel more than 2 metres distance (at least as shown in tightly defined static lab conditions). In one published paper an approved surgical face mask diverted some particles from a sneeze out of the sides and many more particles beneath the chin and down the front of the wearer onto the their chest clothing. This stresses the need to clean exposed clothing after returning home. One justification for wearing any kind of mask is that they must inevitably reduce viral load and that being exposed to lower levels of virus must reduce serious clinical symptoms. But COVID-19 appears easily transmissible and we know little about the virus infectious dose and how it is administered. For example, some influenza strains appear more infectious in large respiratory particles for animal challenge studies while other strains appear more infectious in the much smaller aerosol particles which are more difficult to filter out. If virus is transmitted from contaminated hands to the eyes, nose and mouth then how infectious is this route? There is a lot that needs to be learnt about this new virus.

“The main scenario for the public wearing a mask is in crowded environments where keeping a 2-metre gap is difficult such as stations, trains and buses. Even then, the majority of masks do not protect the eyes which are a known route of respiratory virus entry, suggesting that mask wearers should also wear goggles, like ICU staff. If wearing a mask becomes common then the wearer must recognise that they must not keep touching the mask (because if it is loose fitting then it moves around or irritates the skin). Furthermore, professional surgical masks and respirators are single use items and typically not washable for reuse, while people may be tempted to reuse them because of the cost. If home-made fabric masks are worn, although not advised, they must be carefully removed when entering the home and placed in the washing machine, for a 60oC cycle with detergent, and the hands washed immediately.

“If governments are going to endorse wearing masks then there must be an immediate education program to show the general public how to choose the best quality masks, fit them correctly, wear them for a recommended length of time in a crowded environment and safely dispose of the mask, followed by washing hands. Ideally, eye protection should also be considered. Collateral damage may include making it more difficult for front line staff and emergency responders to obtain the professional masks they really need for their hazardous work.

“People should not become complacent about their hygiene because of wearing any type of mask; they will not become invincible to the virus and must continue to practice rigorous, regular hand washing, cleaning their outer garments and keeping the 2-metre gap wherever possible.”

All our previous output on this subject can be seen at this weblink: www.sciencemediacentre.org/tag/covid-19

Declared interests

None received.