COVID-19 Rates Oscillate Every 6 Months in the US, New Study Shows

COVID-19 cases in the U.S. have shown unexpected oscillating waves every six months between the southern states and the northern states and, to a lesser degree, from east to west, according to research published in Scientific Reports.

Public health scientists from the University of Pittsburgh, University of Ottawa and University of Washington conducted the first detailed analysis to demonstrate and characterize the six-month oscillation of cases across space and time. It provides key information that could inform public health activities, such as vaccination campaigns, that aim to control the virus.

"The COVID-19 winter waves are consistent with that of other respiratory viruses, but the existence of a repeated additional surge during the summer was unexpected," said senior author Donald S. Burke, M.D., dean emeritus of Pitt's School of Public Health.

"These waves start near the southern U.S. border in July and August, when the weather is hottest and the humidity is high—factors that usually tamp down the spread of respiratory viruses. We don't have a good explanation for why COVID-19 rates should increase in both the warmest and coolest times of the year."

The research team, which includes lead author Hawre Jalal, M.D., Ph.D., of the University of Ottawa, and Kyueun Lee, Ph.D., of the University of Washington, believe the data suggest the six-month U.S. COVID-19 waves may be part of a larger pattern sweeping up and down the North American continent.

Further data is needed to test the hypothesis and determine the exact mechanisms fueling these unexpected seasonal oscillations.