I had read that the WHO did not recommend mask wearing in Oct 2019 so I finally looked it up.
In short, there is very little evidence that masks do much good but in a severe epidemic they might help. Epidemic means in one country while pandemic means in multiple countries. ?
I found this Oct 2019 WHO pub on influenza.
https://apps.who.int/iris/bitstream/handle/10665/329438/9789241516839-eng.pdf?ua=1NPI non-pharmaceutical intervention
page 8/91
Available evidence
The evidence base for this guideline included systematic reviews of 18 NPIs, covering:
• personal protective measures (e.g. hand hygiene, respiratory etiquette and face masks);
• environmental measures (e.g. surface and object cleaning, and other environmental measures);
• social distancing measures (e.g. contact tracing, isolation of sick individuals, quarantine of
exposed individuals, school measures and closures, workplace measures and closures, and
The evidence base on the eff
avoiding crowding); and
• travel-related measures (e.g. travel advice, entry and exit screening, internal travel restrictions
and border closure).ectiveness of NPIs in community settings is limited, and the overall quality of evidence was very low for most interventions.
There have been a number of highquality randomized controlled trials (RCTs) demonstrating that personal protective measures
such as hand hygiene and face masks have, at best, a small effect on influenza transmission, although higher compliance in a severe pandemic might improve effectiveness. However, there are few RCTs for other NPIs, and much of the evidence base is from observational studies and computer simulations. School closures can reduce influenza transmission but would need to be
carefully timed in order to achieve mitigation objectives.
Travel-related measures are unlikely to be successful in most locations because current screening tools such as thermal scanners cannot identify pre-symptomatic infections and afebrile infections, and travel restrictions and travel bans
are likely to have prohibitive economic consequences. for pandemic
Moderate
Hand hygiene
Respiratory etiquette
Face masks for symptomatic individuals
Surface and object cleaning
Increased ventilation
Isolation of sick individuals
Travel advice
High
As above, plus
Avoiding crowding
As abordinaryove, plus
Face masks for public
School measures and closures
Extra
As above, plus
Workplace measures and closures
Internal travel restrictions
page 9/91 table 1
Not recommended in
any circumstances [in epidemic]
UV light
Modifying humidity
Contact tracing
Quarantine of exposed
individuals
Entry and exit screening
Internal travel restrictions
Border closure
However, social distancing measures (e.g. contact tracing, isolation, quarantine, school and workpl ace measures
and closures, and avoiding crowding) can be highly disruptive, and the cost of these measures must be weighed against their potential impact. Early assessments of the severity and likely impact of the pandemic strain will help public health authorities to determine the strength of
intervention. In all influenza epidemics and pandemics, recommending that those who are ill isolate themselves at home should reduce transmission. Facilitating this should be a particular priority. In more severe pandemics, measures to increase social distancing in schools, workplaces
and public areas would further reduce transmission.
There is also a lack of evidence for the effectiveness of improved respiratory
etiquette and the use of face masks in community settings during influenza epidemics and pandemics. Nevertheless, these NPIs may be conditionally recommended for ill persons because of other considerations (e.g. the high cost of face masks), and they are generally feasible and acceptable. It is likely that these personal interventions could be effective if implemented in
combination.page 20
Face masks worn by asymptomatic
people are conditionally
recommended in severe
epidemics or pandemics, to reduce
transmission in the community.
Although there is no evidence
that this is effective in reducing
transmission, there is mechanistic
plausibility for the potential
effectiveness of this measure.A disposable surgical mask is
recommended to be worn at all
times by symptomatic individuals
when in contact with other
individuals. Although there is no
evidence that this is effective in
reducing transmission, there is
mechanistic plausibility for the
potential effectiveness of this
measure.
Quality of evidence for above
Moderate (lack of effectiveness in reducing influenza transmission)
page 23
Workplace measures (e.g.
encouraging teleworking from home,
staggering shifts, and loosening
policies for sick leave and paid leave)
are conditionally recommended, with
gradation of interventions based on
severity. Extreme measures such as
workplace closures can be considered
in extraordinarily severe pandemics in
order to reduce transmission.
Quality of evidence for above
Very low
(effective)
