How diseases rise and fall with the seasons—and what it could mean for coronavirus

Scientists and doctors have observed for thousands of years that some diseases, such as polio and influenza, rise and fall with the seasons. But why? Ongoing research in animals and humans suggests a variety of causes, including changes in the environment (like pH, temperature, and humidity) and even seasonal and daily changes to our own immune systems. Figuring out those answers could one day make all the difference in minimizing the impact of infectious disease outbreaks—such as coronavirus disease 2019.