i really like this flu study.

what causes the flu in equator level counties if it isn't from the cold, isn't from being indoors on a seasonal basis and isn't from changes in relative humidity

"Through this, we show that influenza in Vietnam does not show consistent timings, making preparedness efforts such as vaccination campaigns difficult to design."

https://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1011317