Careful. You are correct, but incomplete. It is ABSOLUTE humidity which matters, not relative humidity.

Absolute humidity (the amount of water in the air) is low in winter because cold air doesn't hold as much moisture.

Relative humidity does not depend on temperature since it is a ratio of the absolute humidity to the max absolute humidity at the given temperature.

> It is ABSOLUTE humidity which matters, not relative humidity.

This 2019 paper says that (i) in higher relative humidity, the fine droplets stay larger (larger size after evaporation down to the equilibrium size, given by Kelvin equation) and thus linger in the air for a shorter time. And (ii) higher temperatures, virus proteins denaturate a bit faster. The compound effect of higher relative humidity and higher temperature then makes it look like it correlates to higher absolute humidity.

https://royalsocietypublishing.org/doi/full/10.1098/rsif.201...

Not sure how relevant it is, but influenza (flu) and common coronaviruses (common cold) are not in the same family. Anyways, it seems like it is not a good idea to speculate, even the viruses have closely related:

https://ccdd.hsph.harvard.edu/will-covid-19-go-away-on-its-o...

Also, spreading of flu during "flu season" is marked by holidays when long distance travel happens. This causes slightly different strains of the flu to be brought into regions where people do not have a natural defense to that strain.

Interesting tidbit I learned at a Town Meeting (streamed) yesterday. Winter Break in Massachusetts was instituted to halt the rapid spread of flu during the winter months. Kids would take it into school, spread it among themselves and bring it home to adults, who would get hit harder by it.

The winter break put an an incidental isolation in place that slowed the person-to-person spread down.

This is why schools have to close now to control the spread of COVID-19.

I think you mean February break.

Winter break usually refers to the break that includes Christmas and New Years Day.

In Massachusetts they instituted a second break in February, in addition to spring break in April, in order to cut the flu season.

There is a lot of long distance traveling during summer as well, with all the vacations.

I believe the flu virus is susceptible to UV exposure which may correlate to warmer weather?

As explained to me by an M.D. this is why flu infections go down in the summer

Hospitals worry about many microorganisms besides the coronavirus. It would be unwise to encourage the growth of bacteria and fungi to arrest one virus that can be controlled in other ways.

Some places have humid summers and dry winters, and others have more humid winters and dry summers, like the west coast of the US.

Flu always seems to be during the winter though.

Vitamin D deficiency in winter, close quarters are factors.

From my experience, I have always gotten the flu, or some kind of sickness, after the cold months, as it turns into spring and summer.

When a warmer spring month rolls around, I think that I must’ve escaped getting sick with the flu, then, bam!, I get hit with it, and get knocked out for a few days.

The annoying flu is during the summer, when it’s hot, and you’re sick, so you just become more miserable.