As Colorado slogs through its fourth winter of the COVID-19 pandemic, a curious trend has emerged.

This season — at least so far — the state reached its peak for hospitalizations of people with COVID in the second-to-last week of November. That’s almost exactly when a peak happened last year. And the year before that. And the year before that.

Four years, four different predominant variants of the virus, four different levels of vaccination and immunity in the population. And four times that COVID hospitalizations began rising in late summer or early fall and, more notably, began to decline in Colorado right around Thanksgiving.

“Fascinating and beguiling,” is how Elizabeth Carlton, a professor of epidemiology at the Colorado School of Public Health, described the phenomenon.