Dr. Joel C. Miller Profile picture
Jul 19, 2020 9 tweets 2 min read Read on X
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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More from @joel_c_miller

Dec 16, 2021
So I've got a new preprint out. medrxiv.org/content/10.110… developing mathematical disease models that are appropriate for ethical analysis.

Most of the work done by Daniel Roberts. Help from @ID_ethics, George Heriot, Michael Selgelid, and Anja Slim 1/22
There's some beautiful mathematics in it, but I'll save that for a different thread. Here I'm going to focus on the results.

Our goal is to build a framework that lets us evaluate the ethics of policies for infectious disease policies that try to enforce compliance. 2/x
Let me first say a bit about why this work cannot be applied directly to COVID (not to say it doesn't give insights, but you need to be careful):

We've assumed SIR disease with a single wave. No variants. Importantly, we've assumed that the interventions remain constant. 3/
Read 23 tweets
Aug 27, 2021
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?
Read 8 tweets
Jun 9, 2021
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
Read 13 tweets
Mar 3, 2021
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.

Let's see what data there is to test this...
But, let's clearly state the two hypotheses we'd like to compare and look for the available data and compare their predictions against the data

A) lockdown and fear is responsible for deaths
B) COVID-19 infection is responsible.
First let's look at the people who are dying:

They are dying of a specific set of symptoms that are consistent with respiratory infection, and they are testing positive for a specific virus.

Invariably rise in diagnoses is followed by a rise in deaths.
Read 16 tweets
Feb 6, 2021
Let's talk about how a scientist should make and then test a hypothesis.
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.
Read 11 tweets
Oct 16, 2020
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).
Read 14 tweets

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