Is coronavirus seasonal after all?

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What's That Rash? 11 min 2 speakers 8 chapters transcribed 2 days ago
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Is coronavirus showing a seasonal pattern and what evidence supports it?

Tegan Taylor 0:00
This is an ABC podcast. Hello, this is Coronacast, a daily podcast all about the coronavirus. I'm health reporter Tegan Taylor.
Norman Swan 0:10
And I'm physician and journalist Dr Norman Swan. It's Tuesday the 24th of November.
Tegan Taylor 0:14
So Norman, one of the questions that we've gotten a lot from people about over the course of this pandemic so far is whether it's seasonal. And on one hand, yes, the Melbourne second wave happened in our winter, but it's hard to really tease out what's the difference between seasonality and weather. a new virus in a globe of susceptible people. But in the States, which is going into its winter, and also in other parts of the Northern Hemisphere, we're seeing a really straight upwards curve, a really scary looking curve. So what do we know about the seasonality or otherwise of coronavirus?
Norman Swan 0:50
Well, during the first wave, it was said that there was so much coronavirus around that it swamped the effects of seasonality. Although most people expected this to be a winter virus, a seasonal virus, but they couldn't guarantee it. And you just weren't necessarily seeing the effects of it. On this week's Health Report podcast, I've been talking to Chris Murray, Professor Chris Murray, who's at the Institute of Health Metrics and Evaluation in Seattle. And they've been doing global modelling now on the COVID-19 pandemic, which has turned out to be pretty accurate. So for the world, for different countries and for the United States. And they say that when they look at the big data, they do find a seasonal effect and they believe it's actually quite strong.

How do global models predict a winter peak for COVID‑19 in the United States?

Norman Swan 1:34
And the fascinating thing is that they predict that the virus in the United States will start to peak. Deaths from the coronavirus will peak round about Inauguration Day and tail off towards the end of January into February. So without any vaccine, you will see a natural peaking and tailing off. It won't go down to zero, but it will start to ebb away. If Joe Biden was like Trump, he would take full credit on day two of his presidency for turning around the pandemic, but it will be natural.
Tegan Taylor 2:11
What's the driver for it to peak then? Is it that people are interacting with a certain number of people and you just kind of run out of contacts? How does that peak start to come down again?
Norman Swan 2:20
No, it's obviously a little bit of an effect of natural immunity in that. But even by January, you're still not going to see the majority of Americans infected with the COVID-19 virus. So a little bit of an effect, because what they say is that even 20% coverage of immunity associated with some social distancing could see a tailing off. No, I think they think it's simply how the virus responds to temperature. And although it's still in the middle of winter and pretty cold... There are plenty of viruses that have most of their effect in autumn and early winter and seem to die away in midwinter. In fact, influenza is a bit like that, where influenza in Australia tends to hit more in autumn than in winter, in the depths of winter.

What drives the predicted peak and subsequent decline of cases?

Norman Swan 3:06
Not that we have much depths of winter. So, yep, they think it's seasonal and it might start telling off. And then if we're lucky with the vaccine and the vaccine does prevent transmission, that'll have an even more dramatic effect as the year goes through.
Tegan Taylor 3:18
Yeah, I suppose there were some early, now you mention it, there are some studies that came out earlier in the year saying that the virus survived longer at lower temperatures and in lower humidity. So maybe that's the seasonality thing there. But what does it mean for us in Australia coming into next year's winter if a vaccine isn't widely available by that time?
Norman Swan 3:37
Well, if we've kept our international borders secure and we haven't had too many outbreaks and we're still socially distancing to some extent when we need to and we're able to control, then maybe not very much because there won't be very much virus around. But if there's a significant, say, outbreak from hotel quarantine, if we're still doing it at that point, then you could see a major takeoff. And Victoria, Tasmania, parts of South Australia would be vulnerable to that.

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