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Interplay of Immunity, Climate, and Viral Evolution Explains Semiannual SARS-CoV-2 Dynamics with Implications for
Medrxiv : the Preprint Server for Health Sciences
|March 23, 2026
Summary
SARS-CoV-2 causes two yearly COVID-19 waves in the US, driven by waning immunity and climate. This pattern may persist, influencing future vaccine strategies.
Area of Science:
- Epidemiology and Public Health
- Infectious Disease Dynamics
- Viral Evolution and Immunology
Background:
- Since Omicron's emergence, SARS-CoV-2 has shown persistent semiannual waves in the US, unlike typical annual respiratory pathogens.
- The mechanisms driving this unusual semiannual pattern and its future persistence are not well understood.
Purpose of the Study:
- To investigate the underlying mechanisms of semiannual SARS-CoV-2 dynamics in the US.
- To determine the role of waning immunity, climate, variant activity, and vaccination in COVID-19 hospitalization patterns.
- To predict the future persistence of semiannual dynamics and potential transitions to annual patterns.
Main Methods:
- Utilized a compartmental disease model to analyze COVID-19 hospitalization incidence across 10 US states (January 2022-November 2024).
- Incorporated factors including waning immunity, relative humidity, temperature, variant activity, and vaccination status.
- Performed scenario analyses to explore future dynamic transitions based on immune duration and viral evolution rates.
Main Results:
- Waning infection-derived immunity was identified as the primary driver of semiannual SARS-CoV-2 dynamics.
- Climate factors (humidity, temperature) significantly influenced the timing and magnitude of seasonal waves.
- Summer waves in some states approached winter wave intensity, suggesting localized climate impacts on transmission.
Conclusions:
- Semiannual COVID-19 dynamics, influenced by climate, are likely to persist if infection-derived immunity remains short-lived.
- Durable immunity or slower viral evolution could shift dynamics towards an annual pattern.
- Findings have implications for state-specific vaccination policies, including optimal timing and scheduling for high-risk individuals.
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