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]
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A comment on whether the "Doherty Model" is appropriate if case counts are high when threshold of 70% or 80% is met:
[note - this is my personal opinion without consulting collaborators, should not be taken as official statement of any group I'm affiliated with]
These thresholds provide valuable guidance to policy makers and the public to help them develop plans, and to see that vaccine is the best tool to get us out of our current predicament.
Modelling always involves assumptions, and there is always a risk that an assumption is wrong in a way that materially affects the outcome.
In this case a key question has been raised: might the case count be so high that contact tracing and similar interventions can't keep up?
Why do lockdowns become more important just before or in the midst of a vaccine rollout?
1/n
First, let me both dispel and validate one criticism of lockdowns: "you're just delaying the infections - they will happen later"
2/n
If lockdowns or any other intervention happen but at the same time some immunity builds up, then the epidemic peak will be lower and the total number infected will be smaller.
(seasonal effects may complicate this claim).
Flattening the curve does reduce total infections
3/n
In the thread below, the claim is made that COVID-19 is only hypothetically worse than common cold and that the deaths are a result of lockdown and fear rather than COVID-19.
When one makes a hypothesis, one should look for other, simpler hypotheses which could also explain the data.
In this case, perhaps one might think that the interventions done to control COVID-19 might also control influenza. Since flu has a lower R0, this might be enough.
Another thing a scientist should do is to look for other data that might refute or support the hypothesis.
In this case, perhaps one might look at countries that didn't have a large COVID-19 epidemic. For example Australia and New Zealand.
Some comments on the VIC path to getting its epidemic under control. A 🧵
Victoria hit over 700 cases a day, and now has gotten into single digits per day.
When cases first started doubling each week, there were a few relatively mild restrictions put in. I believed at the time it was an appropriate scale of response. Many felt it was an over-response.
Cases kept growing with a similar rate. More restrictions were put in, and then finally when cases continued to grow, they put in place a fairly strict lockdown (about this time we hit 700 a day).