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Comment by kozak | Hacker News Reader

Why is there higher mortality in winter?

Higher transmissibility of certain viruses could be one reason. If more people are catching it, it's not hard to imagine that more people are getting sick from it, and infecting others. From one study:

> Our study shows an important dependency of SARS-CoV-2 transmission to weather/climate, with each 1°C reduction in mean regional temperature below 10°C leading to a 0.16-unit increase in R0 , or each 1 g/m3 reduction in AH leading to a 0.15-unit increase in R0. Northern hemisphere countries experienced a new wave of SARS-CoV-2 infections during autumnal transition from summer to winter (colder temperatures and lower absolute humidity levels), while still actively maintaining control strategies. When planning to adjust the level of restrictions on social activities, public health strategies need to account for the increased transmissibility of SARS-CoV-2 when/where cold and dry winter conditions are prevalent.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8211690/

It's more likely to be lower levels of vitamin D in winter. Viral transmission is very poorly understood.

Apart from respiratory infections: cardiovascular events. There was a famous paper about guys dropping dead while/after cleaning snow from the sidewalks/driveways (Illinois?). Not necessary from the physical shovelling but from just riding a domestic snowplow. It is good enough be exposed to cold: vessels constrict, blood pressure rises, you may drop dead when old, obese, unfit and with atherosclerosis.

*edit*: article stating that the spikes in mortality were within 3 days of a cold blast. https://academic.oup.com/aje/article/155/1/80/134292

Respiratory illnesses peak in winter. There was always a push for flu vaccinations in the lead up to winter, and now covid in the mix too. https://www.hopkinsmedicine.org/health/conditions-and-diseas...

Why is that in turn? I’ve heard people refer to low vitamin D levels but I’m sceptic if that is the reason (would be so easy to fix)

because that's how the phase locking shook out.

One potential mechanism is people staying indoors more in winter, making all kinds of illnesses spread more easily.

Don’t you dare open that window!

ve must have ze luftink!

Would be interesting to know if Germans have less of a flu season.

Cold affects the immune response.

https://time.com/6238816/why-viruses-spread-in-cold-weather/

Cold temps actually make your nose less effective at fighting off viral infections before they move to your lungs etc. https://www.jacionline.org/article/S0091-6749(22)01423-3/ful...

Lower indoor humidity levels also contribute.

Especially in group 0-14 (higher than during covid) and 15-45 (slightly less than during covid but still more than pre-covid).

Heat kills germs, and from memory SARS-CoV-2 is particularly vulnerable.

Didn't stop COVID from rampaging through plenty of hot places like India.

They have unexpectedly lower excess death from initial covid... Until delta variant comes which isn't fazed at all by summer of 2021.

Indeed, it varies by strain. I was remarking on the initial variant, but I have not followed up on the later variants.

Just means there's more than just heat at play, which is sorta obvious.

Not quite. The cold temporarily weakens our immune systems, particularly in our upper respiratory tract. Couple that with increased proximity to other people in many places when people are more likely to use public transport.

One does not negate the other.

I've not seen studies suggesting that the heat in warmer climates is warm enough to kill off germs in a way that would be relevant. I have seen studies showing the impact of cold on our immune systems. Feel free to provide sources though.

> Mathematical models developed by Seifer & Elbaum (2020) aimed to assess the inactivation of SARS-CoV-2 at physiologically relevant temperatures, i.e. around 40⁰C, and at mild extremes of up to 60⁰C. In cell culture SARS-CoV-2 showed a 99.99% fold reduction in activity after incubation at 56⁰C for 15 minutes, which was in line with the predictions made by the mathematical model, lending some credence to the work. At a normal body temperature of 37⁰C, the model predicts 99.99% inactivation after 48 hours, while a mildly elevated temperature of 39⁰C is expected to induce 99% inactivation at 14 hours, increasing to 99.99% inactivation after 28 hours.

- https://www.news-medical.net/life-sciences/The-Thermal-Inact...

Take that for what it's worth but I honestly thought that this was well known and uncontroversial.

There are other factors, such as the dryness of the heat. But a surface under sunlight in a hot climate could easily hit over 40⁰C

I don’t think you need a hot climate for that. Most surfaces absorb a lot more energy from sunlight than air does, making them hotter than air temperature.

See for example https://web.archive.org/web/20150916052900/http://www.tom-mo..., which has car surfaces hitting 60°C while the air is about 28°C

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