Are we underestimating seasonality?

[sTeamTraen]

Early on in the pandemic, there was (IIRC) a lot of talk/hope that it would die away as the (northern hemisphere) summer arrived. That seemed to get a bit lost over the summer, perhaps because the virus was doing a lot of damage in the warmer parts of the US (notably California, Arizona, Texas, and Florida).

But I'm wondering if there might not be a decent sized seasonal effect. Australia had a flare-up in July. South Africa's curve is almost the opposite of that of most European countries: remarkably low numbers through May, then three very bad months, and now cases have fallen a lot.

Of course, we can tell ourselves stories to fit any narrative, and arguably the rise of cases in Europe started before the equinox, never mind the traditional flu season. And "winter effects" are probably multi-faceted, with factors such as lower temperatures being better for the virus's survival, more people spending time indoors, schools being back, other ailments reducing people's immune response, etc. But I don't see a lot of discussion of this. Perhaps a part of the current upsurge (all over Europe, but also in those parts of the US that had a relatively calm summer; New York now has over half as many cases as Florida) is simply due to this. (Of course, that should also have been planned for, instead of holding "Corona is over" parties, like they did in Prague.)

[jimbob]

The biggest impact of seasonality in this case has to be on people's behaviour.

[shpalman]

Everybody* did seem to say that there'd be a second wave in autumn/winter but where we differ is in the idea that the second wave would be worse if you locked down harder the first time because something something herd immunity.

However, it may be the case that the second wave is worse in places in which the first wave wasn't so bad, because they're taking it less seriously than in places in which the first wave hit really hard. Didn't Israel have its second wave early because it unlocked too quickly and too much after a not-too-bad first wave?

In Italy it's fairly obvious how unlocking over the summer so young people could go to the beach (especially beaches in Croatia) and party caused cases to go up again, but that's nothing compared to what's happening now.

You don't catch a cold from actually being cold but I do think that lower temperatures make people more susceptible to certain kinds of virus, for various reasons, not just being stuck inside with the windows closed.

[Bird on a Fire]

You don't catch a cold from actually being cold but I do think that lower temperatures make people more susceptible to certain kinds of virus, for various reasons, not just being stuck inside with the windows closed.

IIRC there is an effect of having cold air in the nasal cavities or something.

But given that we know outdoor activities are considerably safer than indoor ones (at least during drier months?), the fact that people can no longer sit outsidde/in parks/gardens whatever means that they'll definitely be meeting up indoors instead and infecting each other.

Also, Portugal's just made a new rule that masks are compulsory whenever you're outside of your house, rather than just when you're indoors, or queuing, or in a customer-facing job. This means that when I walk to the shop on a rainy day my mask is soaked, and therefore totally useless, by the time I arrive.

[shpalman]

You don't catch a cold from actually being cold but I do think that lower temperatures make people more susceptible to certain kinds of virus, for various reasons, not just being stuck inside with the windows closed.

IIRC there is an effect of having cold air in the nasal cavities or something.

But given that we know outdoor activities are considerably safer than indoor ones (at least during drier months?), the fact that people can no longer sit outsidde/in parks/gardens whatever means that they'll definitely be meeting up indoors instead and infecting each other.

Also, Portugal's just made a new rule that masks are compulsory whenever you're outside of your house, rather than just when you're indoors, or queuing, or in a customer-facing job. This means that when I walk to the shop on a rainy day my mask is soaked, and therefore totally useless, by the time I arrive.

Get an umbrella or a hat.

[FlammableFlower]

You don't catch a cold from actually being cold but I do think that lower temperatures make people more susceptible to certain kinds of virus, for various reasons, not just being stuck inside with the windows closed.

IIRC there is an effect of having cold air in the nasal cavities or something.

But given that we know outdoor activities are considerably safer than indoor ones (at least during drier months?), the fact that people can no longer sit outsidde/in parks/gardens whatever means that they'll definitely be meeting up indoors instead and infecting each other.

Also, Portugal's just made a new rule that masks are compulsory whenever you're outside of your house, rather than just when you're indoors, or queuing, or in a customer-facing job. This means that when I walk to the shop on a rainy day my mask is soaked, and therefore totally useless, by the time I arrive.

Get an umbrella or a hat.

It's a hoax perpetuated by big brolly - it's all been for just this moment.

[sTeamTraen]

The biggest impact of seasonality in this case has to be on people's behaviour.

But is that any different from why, say, the flu spreads differently in winter? That is, are the relative proportions of the effect of temperatures that are (a) due to a change in favourability for the virus versus (b) due to a change in how people interact, different for COVID than for flu? (And did we ever try to tease those proportions apart before?)

[Herainestold]

A column by a science writer that reaches no conclusion on virus seasonality

When we zoom out from exclusively considering the flu, we realize that not all viruses peak during the winter months. The journal Science put together a nice infographic showing the seasonality of some infectious diseases pre-vaccination. Chickenpox used to peak in the spring. Polio was a summer disease, so much so that swimming was branded as a dangerous activity. And some viruses, like adenoviruses and rhinoviruses responsible for many cases of the common cold, are actually year-round. There cannot be a single explanation or else every viral infection would be in sync. Winter would be the season of illnesses and summers would feel miraculous. Scientists have sweated over trying to identify the many factors that play a role in virus seasonality.

https://www.mcgill.ca/oss/article/covid ... ery-season

[AMS]

Early on in the pandemic, there was (IIRC) a lot of talk/hope that it would die away as the (northern hemisphere) summer arrived. That seemed to get a bit lost over the summer, perhaps because the virus was doing a lot of damage in the warmer parts of the US (notably California, Arizona, Texas, and Florida).

People in very hot places with lots of air conditioning might well spend more time indoors together in summer than in winter.

[sTeamTraen]

Early on in the pandemic, there was (IIRC) a lot of talk/hope that it would die away as the (northern hemisphere) summer arrived. That seemed to get a bit lost over the summer, perhaps because the virus was doing a lot of damage in the warmer parts of the US (notably California, Arizona, Texas, and Florida).

People in very hot places with lots of air conditioning might well spend more time indoors together in summer than in winter.

Good point. Also, American AC tends to run at the kind of temperatures that the virus (and, indeed, fresh milk) likes.

[raven]

There is a nice clear summary of what is known about coronaviruses and seasonality here:
https://coronavirusexplained.ukri.org/e ... 0009/#ref2

With links to papers about this stuff. Figure 2 in this one shows previously circulating human coronaviruses usually peaked between December and April in the Northern Hemisphere. Slightly later than flu.

Covid-19 doesn't fit that pattern, I think because it's novel and there's no prior immunity.

[sTeamTraen]

Huh. I just realised that there already was a seasonality thread before I started this one. Apologies for any confusion caused.