Discussion
We have modelled the potential impact of the use of face coverings worn
in retail outlets and on public transport on the number of UK COVID-19
infections and associated hospital admissions and mortality rates.
Overall, we demonstrated that only around 7% of all community-based
infection risk for those aged more than 16 years of age is associated
with public transport and retail outlets. This contrasts with 57%
associated with work or study, for those aged 16 years and over. This
illustrates the limitations of the impact of any policy to reduce
infections in the public transport and retail outlets sectors alone,
irrespective of the efficiency of the intervention. It perhaps suggests
that measures targeted at the workplace may be more worthwhile.
In addition to this, the requirement to wear face coverings may increase
anxiety in some people and thereby result in a reluctance to utilise
public transport and/or visit retail outlets. This may, therefore,
reduce the time spent on these activities. While it is also possible
that the use of face coverings may increase the confidence of other
people, it is difficult to say whether this will negate the above
effect. Certainly, public transport usage and retail footfall does not
appear to have returned to pre-pandemic
levels,27,28 and
hence the 7.3% may be an overestimate of the contribution of these
activities to overall risk. However, in our modelling, given the
difficulty in calculating this impact, we assumed this change in
behaviour to be neutral.
For the determination of the impact of face coverings on reduction in
infections, we used a range of R values to allow estimation of the
potential change in the impact of face coverings in different phases of
the pandemic that are relevant at this stage. The impact of any
mitigation measure will have a more significant impact, at least in
terms of overall numbers, the higher the R-value. We showed that, with
an R-value of 0.8, with face covering of 40% effectiveness, average
infections would be reduced by 844/week, hospital admissions by 8/week
and deaths by 0.6/week; a fall of 9% over the period total. If,
however, the R-value rises to 1.0, then average community infections
would stay at 29,400/week and face coverings could reduce average weekly
infections by 3,930, hospital admissions by 36/week and deaths by
2.9/week; a 13% reduction.
These reductions should be seen in the context of the reality that 93%
of adults had worn face coverings when shopping in the seven days to 21
August 2020 30 .These figures should be viewed with
the perspective that there were a total of 437,500 emergency admissions
reported 31 in June 2020, 17.3% lower than the same
month last year and that all-cause deaths at the start of August 2020
were reported32,33,34,35 at 1,270/day, of which 490
occurred in hospital.
This raises interesting questions around the timing of the
implementation of the policies to mandate the use of face coverings in
the retail and transport contexts; a time when the R-value was less than
one (most UK government reports suggested 0.7-0.9) and the daily
infection rate was relatively low in comparison to the peak in April
2020.29 Use of face coverings in retail outlets and on
public transport is of limited value, particularly when the R-value is
below 1, in contrast to March/April 2020 when the R-value was much
higher.
We also used a range of efficiencies of face coverings, reflecting the
wide range of types of coverings,1 variability in
correct usage (particularly over prolonged periods) and uncertainty
around which modes of transmission could be influenced by their
use.21 Realistically, an estimate of around 40% is
likely to be a sensible conservative estimate, particularly in the
context of the work by van der Sande et al.23 Under
this assumption, the modelling showed that, if the R-value was 0.8, the
hospital deaths avoided would be less than 0.1/day and if, in the
extreme case that R-value rose and stayed at 1.2, this could rise to 2
deaths/day avoided.
This study shows that face coverings, even when appropriate materials
are used, and handling and wearing are fully compliant, can only
generate limited benefits when used at low reinfection rates. By
preventing potential future infections, they may play a more important
role at times when reinfection rates are high.
Given our findings, we suggest that guidance on the potential usefulness
of face coverings might benefit from greater clarity of guidance that is
better targeted to those most likely to benefit, and in activities where
the impact is likely to be larger. For example, the availability of more
effective, surgical standard face masks (with clear guidance on correct
use) for those more vulnerable to serious consequences of infection, and
in contexts where they are at greater risk (such as in the workplace)
might be of greater impact in terms of reduction in hospital admissions
and deaths.
This approach might also minimise the mental health consequences of
widespread use of face coverings36, including by
sending a more reassuring and realistic message to the population around
risk. It may also encourage economic activity both in terms of high
street spending and return to work.
Finally, these findings in no way relate to the use of approved face
coverings in the care of vulnerable, frail and older individuals in the
care home, hospital or primary care setting.
Strengths and Limitations
We recognise that such modelling is based on a range of assumptions. To
address this, we have sought to use UK government/ONS data wherever
possible, as these are the data that are likely to have been used to
inform policy. We have also erred on the side of caution in our
estimates. Where estimates may differ widely (such as for face-covering
efficiency in reducing transmission), or subject to change (such as
R-value or number of daily cases), we have presented a range of
scenarios to give a sense of the impact of face coverings at various
levels of R face-covering effectiveness.
Conclusion
We have illustrated that the policy on mandatory use of face coverings
in retail outlets and on public transport in the UK, may have limited
value in reducing hospital admissions and mortality rates, at least
given the time that it was introduced.
We suggest that a National Institute for Health and Clinical Excellence
(NICE) review is merited, assessing the cost-effectiveness of the use of
face coverings as a clinical intervention alongside other preventative
measures, as a means of reduction in hospital admissions and indeed
mortality.
Table 1. The contribution of different activities on
Infection Risk Score and the impact of face coverings on infection risk
Table 2. Projections for average weekly values over the
3 months from the introduction of mandatory face coverings on