Scott Alexander examines theories for disease seasonality, proposing a dynamic model where seasonal factors entrain waning immunity cycles.
Longer summary
Scott Alexander explores the seasonality of diseases, particularly focusing on flu and COVID-19. He discusses various theories for why diseases peak in winter, including cold temperatures, low humidity, indoor crowding, and vitamin D deficiency. He finds these explanations unsatisfactory and proposes that ultraviolet light might play a role. Scott then considers a dynamic model where disease immunity wanes over time, and seasonal factors entrain this cycle to create annual epidemics. He suggests that COVID-19 is currently in a 'half-seasonal' phase and may become fully seasonal once it has infected most of the population and exhausted easy mutations.
Shorter summary