Medical and Scientific DUers: Why does the influenza virus have a "season"?

[milestogo]

What is it about a virus that makes it more active during some times of the year than others?

Is it weather dependent?

People are assuming that the COVID-19 virus will have a season that comes to an end soon... is there any reason to think this is true?

[BusyBeingBest]

1. I've seen arguments that people are together more in confined spaces

in winter, and that viruses can be sensitive to heat. But neither of those explanations ever seemed plausible to me.

[bearsfootball516]

2. My understanding was that flu/illnesses are much more prevalent in the winter

Because people are cooped up in their homes and have very little fresh air, which basically causes homes to become breeding grounds for germs.

[at140]

5. Yes we shut windows tight when it is cold outside

and that means breathing stagnant air.

[Laffy Kat]

17. Yes, I from what I understand influenza prefers dry air. nt

[LisaL]

3. Flu viruses are more stable in cold air and low humidity.

[krispos42]

14. That's my understanding

Humidity makes water cling to the flu virus, so it's heavier and falls out of the air sooner.

[dhol82]

4. I think it's more 'close quarters' dependent .

When it’s cold we cluster together. When it’s warm we separate.
It also gives a virus a several month window to mutate.

[5X]

6. Covid-19 is spreading worldwide, would think temp is not important. n/t

[milestogo]

7. In African countries where several viral diseases are prevalent

the weather is warm and people are seldom cooped up inside. Some of these are mosquito borne, but not all.

[Igel]

18. It's not a question of if, it's a question of how much.

I've had colds and seen the flu in summer. It's a question of frequency.

For flu, there are two competing views. The first is that temperature and humidity work to help degrade the virus; the second is that dry, cold temperatures help prep the mucosal lining for easier infection. The second is more aesthetically pleasing, but I the last I heard opinion was it was the former, virus degradation.

It would be interesting when there's enough data to see if temperature does play a role with COVID-19, whether seasonally or by geography. There *are* cases in warmer climates, but it may be that in the end there are far fewer than you'd otherwise expect. Stay tuned for research next year.

Not that colds always follow the same pattern. And there's a claim that's mostly behind a firewall that COVID-19 is transmitted most efficiently at "8.72 degrees C" (I find the number of significant figures there amusing, given that everybody who's contracted the virus is transmitted is subject to a temperature range throughout the day, whether indoors, outdoors, or alternating).

[Quixote1818]

8. I think it has to do with the air being more dry in the winter and lower levels of vitamin D

from people staying out of the sun.

[djg21]

9. Humidity

https://www.livescience.com/27533-flu-transmission-humidity.html

[lapfog_1]

10. according to a study I read

there are a number of reasons:

1. Some viruses are susceptible to warmer weather meaning they don't live as well on surfaces which are warm to hot.

2. Most if not all viruses are susceptible to increase UV radiation... longer hours of sunlight, reduced viral activity.

3. Colder weather impacts are own natural immunity (we have none for Covid-19).

4. Warmer weather means people are outdoors more, more sunlight, more vitamin C, less contact with strangers in enclosed spaces.

It is that very last point, people not interacting with others as much, that might be the largest component of "flu season" but most likely it is the combination of factors.

Yet to be determined if Covid-19 will reduce due to warmer weather, so far the results from warm weather locations like Indonesia are not promising. MERS, another corona virus, was not a season sensitive virus.

[Quixote1818]

11. Here you go

[milestogo]

13. Thank you.

[jberryhill]

12. Several factors

Heated air is dry and reduces the effectiveness of your mucous membranes at providing a barrier. People are cooped up. The virii do better in cold dry air....

Here’s a summary:

https://www.popsci.com/cold-flu-season-sick-winter/

Keep an eye on how Australia, Chile, Argentina, and South Africa are doing.

Now, there is a lot of movement between Australia and relatively nearby Asian countries, and there are cases in Australia. The thing to watch is if there is a significant spread in places like Adelaide, Melbourne, etc.

[Spider Jerusalem]

15. It is spreading in Australia where it is currently summer

assuming it has a "season" is wishful thinking.

[Wounded Bear]

19. Also cases in the tropics...So America and Africa...nt

[NickB79]

16. MERS spread in the Middle East in 100F weather a few years ago

And it's a related coronavirus to COVID.