Changes to Endemic Respiratory Virus Circulation and Testing Before, During, and After the COVID-19 Pandemic

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The COVID-19 pandemic significantly disrupted the circulation of endemic respiratory viruses, particularly winter-dominant types like influenza A and RSV.
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Winter viruses experienced sharp declines in positivity during the pandemic, with prolonged recovery times compared to spring and year-round viruses.
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Spring viruses, such as parainfluenza 3 and human metapneumovirus, quickly returned to prepandemic positivity levels within two seasons post-emergence.
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Altered seasonality patterns were observed, with influenza A transitioning to a semiannual pattern before normalizing in 2024.
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The findings highlight the need for future pandemic preparedness, as the degree of disruption varied based on the overlap of virus circulation with SARS-CoV-2.

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