Peak Nasal SARS-CoV-2 and Influenza Viral Loads Relative to Symptom Onset, 2022–2025: Impact of Vaccination and Implications for Multiplexed Testing

In 2023-25, median SARS-CoV-2 VL peaked earlier relative to symptom onset compared to a highly immune 2022-23 cohort. More recent vaccination correlated with delayed peak VL, suggesting more robust immunity correlates with earlier symptom onset relative to peak. Median influenza A VL were highest at symptom onset, versus 4 days into symptoms for influenza B. These findings can inform use of multiplexed antigen tests amidst changing immunity and viral circulation patterns.