Thread by @PatrickSSte

I've noticed that explanations for resp-vir seasonality involving humidity are becoming more popular

Eg doi.org/10.1101/2020.0… by @EdsardRavelli
1/

The problem is that we essentially have ONE observation - that hundreds of often unrelated viruses in all regions (outside the Tropics) with very diverse climates, have winter seasonality
2/

If we say the winter surge of colds in one place is due to eg school buses, business travel and humidity, but somewhere else it's sports events, snow and sunshine, we are cheating. We’re “overfitting” - we are using too many variables to model a 1-d phenomenon
3/

So we’re looking for one main factor that drives seasonality – maybe two.

Seasonality COULD be driven by temperature and humidity, 50: 50. That is possible, although it would be a coincidence.
4/

Can we seriously propose that dry air is the main driver all over the world? It doesn’t work well. For example, it’s much drier in Mediterranean countries in summer, but of course they have colds in winter
5/

Another problem for humidity is that respiratory infections tend to surge in the AUTUMN - before humidity has really changed. See examples below.

But temperature has dipped
6/

I'm not saying that humidifying your house isn't a great idea, or that it has no effect on viruses. Just it's not the main driver of seasonality.

It's a problem that temperature and humidity are so closely correlated - which is why we need experiments (see our paper)
7/

Bear in mind that winter seasonality isn't a new phenomenon. Eg here is flu 1964-75, when many people had poor heating and no air conditioning
8/

My point is, if you stand still outside for more than 2 mins in winter and get chilled, you are in some danger of dying from a respiratory infection.

But if you dress up warmly and go skiing and breath this cold dry air which we are told is so dangerous . . . you feel fine!

All explained in our paper, written with @JuliaLBach8

doi.org/10.1002/rmv.22…

I forgot to say, the theory that says that dry conditions produce finer aerosols containing virions, which are more stable, doesn't work in the Tropics

Influenza and colds both arrive in the RAINY season in Fortaleza and Singapore. This is also true in eg India Indonesia

This hospital in Bangkok believes that the problem is chilling

bangkokpattayahospital.com/en/healthcare-…