Why the Flu virus is seasonal
Summarizing this article from TIME, there are three main reasons why the Flu is (mostly) seasonal:
- The virus is more stable and can remain airborne longer in cold, dry air.
- People stay inside more when it’s cold, where they quickly become vitamin-D deficient.
- When people are inside more, they are in closer and more regular contact with other infected people.
Countries with a perpetually tropical climate have consistent rates of infection all year long.