AFTER COVID-19 measures eased, flu symptoms aligned with revived winter peaks for RSV and Influenza A.
Flu Symptoms Signal Seasonal Reset
A retrospective observational study tracked respiratory infections as non-pharmaceutical interventions (NPIs) related to COVID-19 were lifted, using respiratory multiplex testing from October 2021 to December 2024. Investigators analyzed 307 patients tested with multiplex PCR at a single laboratory in Lebanon, comparing the NPI period (October 2021 to May 2023) with the post NPI period (May 2023 to December 2024).
Across the post NPI period, most respiratory viruses reestablished seasonal patterns that resembled pre pandemic circulation. For clinicians evaluating flu symptoms, the key shift was the return of characteristic winter peaks for respiratory syncytial virus (RSV) and Influenza A, supporting a renewed expectation of wintertime clustering after the rollback of masking, distancing, and other containment measures.
Rhinovirus Dominance and Viral Interference
Rhinovirus remained the most prevalent pathogen across the study window. The authors suggest this persistence may relate to the absence of a vaccine, implying continued high background circulation even as other viruses regained seasonality.
The study also reported that human metapneumovirus (HMPV) appeared without co infections, a pattern interpreted as consistent with viral interference. In this framework, infection with one respiratory virus may transiently reduce susceptibility to another, shaping observed co infection patterns during periods of changing population level exposure.
Multiplex PCR Testing in Post NPI Respiratory Infections
Influenza A and SARS-CoV-2 persistence appeared to be influenced by factors including vaccine coverage, viral mutations, and environmental conditions. The authors highlight multiplex PCR as a valuable tool for diagnosis and epidemiological surveillance, while emphasizing that cost may limit access.
Taken together, these findings reinforce the importance of ongoing viral monitoring after NPIs, both to support clinical decision making when patients present with flu symptoms and to guide public health planning as seasonal respiratory infections continue to recalibrate.
Reference: Keyrouz R et al. A New Breath: Dynamics of Respiratory Infections After the Lifting of Non-Pharmaceutical Interventions Related to COVID-19. Microorganisms. 2025;13(12):2710. doi:10.3390/microorganisms13122710.
