Forcing Seasonality of Influenza-like Epidemics with Daily Solar Resonance

Seasonality of acute viral respiratory diseases is a well-known and yet not fully understood phenomenon. Several models have been proposed to explain the regularity of yearly recurring outbreaks and the phase differences observed at different latitudes on the Earth. Such models consider known internal causes, primarily the periodic emergence of new virus variants that evade the host immune response. Yet, this alone is generally unable to explain the regularity of recurrences and the observed phase differences. Here we show that seasonality of viral respiratory diseases, as well as its distribution with latitude on the Earth, can be fully explained by the virucidal properties of UV-B and UV-A solar photons through a daily, minute-scale, resonant forcing mechanism. Such an induced periodicity can last, virtually unperturbed, from tens to hundreds of cycles, and even in the presence of internal dynamics (host's loss of immunity) much slower than seasonal will, on a long period, generate seasonal oscillations.