COVID-19 May Follow a Different Seasonal Pattern Than Influenza, RSV, P2

By Sabrina McCrear

Fact checked by: Maggie L. Shaw

June 29, 2026

Source: AJMC

Photo / Image Source: Unsplash,

Regional Climate and Human Behavior May Help Explain Summer COVID-19 Transmission

Additional research has shown that COVID-19 transmission frequently oscillates between northern and southern regions of the US throughout the year. During the summer months, increases have historically been observed in southern states, including Texas, Louisiana, and Mississippi, before shifting northward during the winter months.⁶

Rather than warm weather itself driving transmission, researchers suggest that seasonal behavioral and environmental factors likely contribute to these regional differences. High temperatures and humidity often encourage people to spend more time indoors in air-conditioned environments where prolonged close contact may facilitate viral spread. Summer travel, gatherings, and declining immunity from prior vaccination or infection may also contribute to seasonal increases.⁶

These observations differ from influenza and RSV, which remain predominantly winter respiratory viruses despite occasional fluctuations in timing. Influenza transmission is favored by colder, drier conditions, while RSV typically peaks from late fall through winter. In contrast, SARS-CoV-2 continues to exhibit a more flexible seasonal pattern that appears to be shaped by viral evolution and changes in population immunity in addition to environmental factors.

Researchers caution that these recurring patterns should not be interpreted as fixed predictions. The timing and magnitude of future COVID-19 waves will continue to depend on the emergence of new variants, population immunity, vaccination uptake, and local environmental conditions. Nevertheless, the findings underscore the value of wastewater surveillance as an early warning tool that can detect increasing viral circulation before clinical cases begin to rise, allowing health systems and public health officials additional time to prepare.

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