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How does the timing of influenza symptoms differ from the timing of COVID-19 symptoms?
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influenza
A colored transmission electron micrograph showing influenza viruses (red) at the outer surface of a host cell.
The timing of symptom onset is a key difference between influenza and COVID-19.
- Influenza: The incubation period for the flu is typically one to two days. Following this, the onset of symptoms is characteristically abrupt, manifesting as sudden chills, fatigue, and muscle aches.12
- COVID-19: Symptoms of COVID-19 generally take longer to emerge, appearing anywhere from two days to two weeks after exposure.34
While both are contagious respiratory diseases that can cause similar symptoms such as cough and fever, the rapid, distinct onset of the flu contrasts with the broader and more variable timeframe associated with COVID-19. Because these illnesses can present similarly, testing is the most reliable method to confirm the specific cause of a respiratory infection.35