How do you tell flu from RSV?
Last updated September 3, 2026.
Flu typically hits suddenly with fever, aches, and exhaustion, while RSV usually builds gradually like a cold - runny nose, congestion, cough, and its signature wheeze. But be honest with yourself: the CDC notes RSV symptoms overlap heavily with colds and flu, so symptoms alone often cannot settle it. Both circulate in fall and winter, RSV peaking around December and January. The stakes differ by person - RSV is mild for most healthy adults but is the leading cause of bronchiolitis and pneumonia in infants under one and hospitalizes older adults - so for those groups a clinic swab panel (flu, RSV, COVID) is worth it. Pymander is a free AI doctor, 24/7 by text, and can help you read the pattern.
What to do
- Judge the onset: sudden flattening points to flu; a slow cold-like build points to RSV.
- Listen for wheeze: RSV moves into small airways - wheezing is its tell, especially in babies.
- Test when stakes are high: infants, older adults, and the immunocompromised deserve a real swab.
- Watch breathing in little ones: fast breathing, chest retractions, or poor feeding mean same-day care.
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