A regarding facemasks (now required in Melbourne).

We've been seeing 200-400 cases a day for about a week now.

I've been wearing a mask in public for a while now. I think they are an important additional step for disease control.

Ultimately our most important control is contact tracing.

To make contact tracing more efficient, we need to limit the hard-to-trace contacts, such as might occur in a grocery store/restaurant.

The hardest clusters to control are those that just appear out of nowhere.

Masks help reduce these.

!!!HOWEVER!!!

Masks are not perfect. You probably won't wear it perfectly.

Their main benefit is to prevent droplets from your mouth/nose reaching others, they do less in the other direction.

So those people you see not wearing masks? Not covering their nose? Not fitting quite right?

They remain a danger to you even if your mask is perfect.

And even those who wear it perfectly are still a possible source of infection to you.

The adverse effect we (epidemiologists) worry about is that the public starts to view masks as an invisible force field.

It's not. If you get virus on your hands and rub your eyes, the mask won't help.

So the rule I've been using while wearing a mask is the following:

If the activity is important enough that I would do it without a mask, I go ahead and do it but wear a mask and hope others do too.

Otherwise, I don't do it.

Don't let wearing a mask make you think you've become invincible.

[and a disclaimer - while my job is to study infectious disease control, I have no special expertise on masks. I'm relying on what I've learned from others I trust for what I say here]