For the northern hemisphere it’s much less humid in winter, but that’s not true everywhere.
https://www.livescience.com/27533-flu-transmission-humidity....
We really should be increasing humidity in hospitals and offices in the winter. Newer planes have already been moving in that direction (to increase comfort).
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.
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...
https://ccdd.hsph.harvard.edu/will-covid-19-go-away-on-its-o...
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.
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.
As explained to me by an M.D. this is why flu infections go down in the summer
Flu always seems to be during the winter though.
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.