We do not yet understand seasonality in viruses. There are ideas about UV from sunlight zapping them. There are ideas about elevated vitamin D in humans during the warm season. There are ideas that warm weather just dries them out, that they can’t handle the osmotic pressure of higher humidity, and that melatonin based human immune seasonality and virus seasonality co-evolved.
In general, coated viruses are seasonal. Covid-19 is coated. Three human coated corona viruses that commonly circulate as colds are strongly seasonal. We show below the seasonality of past U.S. Pandemics.
These deaths are not adjusted per capita, as that has no effect on seasonality and separates the curves. Clearly, prior pandemic deaths are strongly seasonal. The 1967-68 year looks like it may have been pretty bad. Unfortunately, CDC has no monthly data except for 68-69.
Corona got off to a very late start in the U.S. Will it go “away in May”? Nobody will write a guarantee as this virus has been breaking rules. If it does, it may be back very strong next fall. We should have a vaccine by then.