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RSV vs Flu vs Cold: How to Tell the Difference

  • Writer: Sam Ahn
    Sam Ahn
  • Oct 26
  • 2 min read

Written by Dr. Sam Ahn, MD (Family Medicine Specialist, Medical Contents Director of MoDoc AI) | 2025-10-21


Last winter, 280 American children died from flu - 89% were unvaccinated. As RSV and flu surge together this fall, here's what every parent needs to know.



What's the Difference?


RSV (Respiratory Syncytial Virus) is the "mucus and breathing trouble" virus. It produces massive amounts of thick mucus and can make breathing difficult, especially in babies under 2. Starts like a cold but worsens around days 3-5 with a whistling wheeze.


Flu (Influenza) hits like a truck - fine in the morning, then 103-104°F fever with severe body aches by evening. Kids can't get out of bed.


Common cold has mild symptoms. Kids stay relatively playful.


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Prevention Saves Lives


Get your child vaccinated. Flu shots for everyone 6+ months old (best before Halloween). For RSV, babies under 8 months need antibody injections. Since RSV vaccination started, infant hospitalizations dropped 43%.



Home Care


These are viruses - antibiotics won't help. Keep your child hydrated with frequent small sips of water. Use a humidifier. For RSV, clear the nose with saline drops and gentle suctioning before feeding.


Use Tylenol (3+ months) or Motrin (6+ months) for fever. Never give aspirin to children.



Rush to the ER If You See:


Breathing emergencies:

  • Skin sucking in between ribs when breathing

  • Nostrils flaring or grunting sounds

  • Blue/gray lips or face

  • Extremely fast breathing


Severe dehydration:

  • No wet diapers for 8+ hours

  • No tears when crying


Other emergencies:

  • ANY fever in babies under 3 months

  • Can't wake your child

  • Seizures

  • Fever over 104°F that won't come down



Summary


RSV = mucus and wheezing. Flu = sudden high fever and body aches. Watch for breathing trouble and dehydration. Vaccines aren't optional - they're lifesavers.


Trust your instincts. You know when something's seriously wrong with your child.



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Dr. Sam Ahn is a board-certified family medicine physician and medical advisor for MoDoc AI's FeverCoach. This article is for educational purposes and does not replace professional medical advice.

 
 
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