Thread by @AndrewNoymer

Let's talk seasonality and #covid19 #nCoV2019 #coronavirus.

There is an element of seasonal roulette with emerging viral diseases.

I have previously said #OnHere that China had a stroke of bad luck to have emergence in December, just as the flu season was getting underway.

The reason I mentioned before was that flu competes for space in hospitals, and causes Dx problems.

But there is another reason: flu and *all* respiratory viruses spread more in the wintertime.

Even measles — a rash, but which has respiratory transmission — is winter-dominant.

By emerging at the start of the N Hemisphere winter, the coronavirus #covid19 #nCoV2019 has all the advantages (to it) of the winter season. Not just confusion with flu, but the enhanced transmission that the winter brings to respiratory viruses.

There are many hypotheses about why viruses spread better in the winter. Temperature, relative humidity, absolute humidity, outdoors UV, contact patterns (especially school); and, others. The truth is we don't know for sure why viruses are so seasonal in the temperate regions.

It's not a basic cold effect. There is plenty of lab-confirmed flu in tropical regions, altho #influenza follows a less regular epidemiological pattern in the tropics.

Getting back to the matter at hand, #coronavirus #nCoV2019 #COVID19 and the timing of its emergence...

December is unfortunate timing. It's seasonal roulette and we lost. SARS in 2003 emerged slowly but really explolded in March. This may partly explain why it wasn't worse. Very-late-winter emergence. The universe is not some lab experiment we can re-run, but season matters.

In #flu pandemics, we see the same thing. The novel H1N1 flu #pandemic of 2009 emerged in N America in April. Spring. Good timing. It mostly took the summer off, only to make a bad (and unusually early) 2009–10 flu season, starting in October 2009. But it wasn't catastrophic.

The summer of 2009 (again, N. Hemisphere) gave a bit of breathing room in the most-recent flu #pandemic. There was something similar in the much-more-deadly 1918 pandemic, with the first and second waves having summer between them.

What does this mean for #nCoV19 #covid19 #CoronarvirusOutbreak? The situation is still fluid.

It's now mid-February. The days are getting longer in the N Hemisphere..

The timing of emergence was about as bad as possible, but we are heading towards spring.

So two takeaways, I think, are these:

(1) In China... as bad as it is, the seasonal change is heading in the direction of making things better. Hold on, spring is coming! Viruses become less transmissable in the spring/summer vs. fall/winter.

(2) in the temperate N Hemisphere, outside China... spring is coming. We have so far avoided the brunt of the #nCoV19 #COVID19 outbreak till now... every week that passes is another week closer to spring/summer, and brings a sigh of relief. Less transmission risk!

If (ex.) N. America avoids the worst for another 4 weeks, it will probably avoid the worst, alltogther.

– Summer lull should be treated as an opportunity to re-alloy preparedness.

– Vigilance should be kept for a fall wave of #COVID19 #nCoV19 in all of temperate N Hemisphere

There are some obvious corollaries, mutatis mutandis, for the temperate Southern Hemisphere.

I'll leave it there for now. Thank you for reading this thread on #seasonality and respiratory-virus epidemiology. #pandemic #CoronavirusOutbreak #COVID19 #coronavirus #preparedness