A new study led by researchers from the Wayne State University of School of Medicine has revealed a trending seasonality to yearly COVID-19 surges, specifically two smaller peaks in the spring and summer, and the largest peak in the winter.

“Our study also revealed that climatic factors, such as temperature and rainfall, do not play a driving role in the seasonality of COVID-19 outbreaks. The timing of COVID-19 incidence outbreaks was not affected by vaccination campaigns, and did not directly correlate with public holidays or environmental factors,” said study co-author Kezhong Zhang, Ph.D., a professor of Biochemistry, Microbiology and Immunology and of Molecular Medicine and Genetics.

The study has immediate implications for both public health professionals and the public at large in understanding and preparing for future COVID-19 surges.

In Seasonality of COVID-19 incidence in the United States, published in the journal Front Public Health, they outline a predictable seasonality of COVID-19 outbreaks in the U.S. The seasonality is characterized by the waves of COVID-19 incidence occurring three times a year.

The team collected daily county-level COVID-19 incidence data across the contiguous U.S. for three full seasonal years, from March 2020 to March 2023. The data was sourced from reliable databases such as 1Point3Acres and The New York Times, which are known for accurate, real-time updates of COVID-19 cases and deaths. The core methodology the authors employed in the study was spectral analysis using Fast Fourier Transform algorithms.

“Our findings of tri-annual peaks in COVID-19 outbreaks could be very useful in public health preparedness. For instance, authorities can allocate resources more effectively and implement targeted public health interventions to counter anticipated surge periods,” Dr. Zhang said.

“However, it is important to recognize that though the public health/social/environmental factors did not affect the timing of the outbreaks, they likely have a significant impact in the amplitude of each outbreak. For example, vaccination and social distancing/mask-wearing efforts are the likely reason for significantly lower amplitudes of each outbreak in the second year of the pandemic (2021-2022) compared to the first year (2020-2021).”

Class of 2023 graduate El Hussain Shamsa, M.D., an Internal Medicine resident at Case West Western/University Hospitals in Cleveland, contributed to study, including while working Dr. Zhang’s lab as a medical student at WSU.

The study first acknowledges a debate over whether COVID-19 disease incidence follows a seasonal pattern like many other respiratory viral infections, such as influenza. The identification of seasonality of COVID-19 is crucial for infection control as it can guide public health prevention measures.

The publication and the related results were featured by Medicine Innovates as a research breakthrough, and the article Seasonal Patterns and Periodicity of COVID-19 Outbreaks in the United States: Discoveries from a Spectral Analysis Study.