The acrimonious debate about masks between usually sensible people seems unhelpful. Those in the “no evidence, need an RCT, they do harm” camp seem over-anxious, and those saying they are the most important thing are over confident.
1/n

I think that there is reasonable evidence that they reduce transmission. Not from RCTs (but then that is not the right design for complex non-pharmaceutical interventions in my opinion) but from real world experience, plausibility, case studies and in lab simulation studies. 2/n

I think that even if the effect is relatively small in terms of transmission probability, that will help at the population level, as will hand washing.3/n

Remember, the reproductive number R is determined by 3 parameters in the population:
c - number of contacts
D - duration of infectiousness
b - probability of transmission from infected to susceptible.

Any intervention that reduces any of them will reduce R
4/n

Masks may have a relatively small effect on b, it together with increased physical distance and better ventilation it is likely to be important. And in some situations with a high probability of transmission (e.g. health & social care) the reduction could be crucial. 5/n

So what about the harms? There are harms and we shouldn’t deny them.
Masks impede communication which can damage relationships and mental health.
They are particularly difficult for people with hearing loss and people with autism.
Some people get anxious about breathing
6/n

Masks may lead to disinhibition- people wearing them /seeing others wear them may be less likely to adhere to recommended distancing. Some people may touch them, wear them incorrectly and reduce hand hygiene.

So yes, these are possible harms. However, many can be mitigated
7/n

Most people can learn to wear them, and we need training in breathing and communication for those who find it hard.

We need investment to develop new effective transparent masks to allow lip reading - if we can design an invisibility cloak surely we can do this?

8/n

And to those who are “pro-mask” ?
Please don’t be messianic.

The “shame them & fine them” approach will not help - it’s stigmatising. Criminalising individual behaviour is not effective public health (IMHO).
Educate & encourage instead.
9/n

Finally, condoms.
)No, don’t use them in place of a mask... )
But...
- Condoms are not 100% effective (probably a lot better than masks to be fair)
- there is poor RCT evidence of population impact
- but their widespread adoption reduced in STI and HIV eg in 1980s

10/n

Widespread adoption of an imperfect intervention can have an important population effect.

So....
Let’s try and make masks cool, fun, sexy

Let’s support people who find them difficult.

(“Some people can’t wear masks. Get over it” )

And please, above all, be kind.

ENDS