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Help! My Baby Has a Fever After Vaccination Shots!

  • Writer: Sam Ahn
    Sam Ahn
  • 6 days ago
  • 2 min read

Written by Dr. Sam Ahn, MD (Family Medicine Specialist, Medical Contents Director of MoDoc AI) | 2026-01-08



Watching your little one cry during shots is hard, but a fever afterwards can feel even scarier. You might worry something is wrong, but take a deep breath—you are doing great.


Why the Fever Happens


A fever is actually a sign the immune system is working. Think of it as "boot camp" where the body trains to fight viruses. This training creates heat, causing a fever that usually starts within 24 hours and resolves in a day or two. It is most common around the 4-month and 12-month milestones.



Is It the Shot... Or Is My Baby Sick?


It can be hard to tell the difference, but here is a quick breakdown.


It is likely the vaccine if:

  • The fever starts within 24 hours.

  • It lasts less than two days.

  • The baby is fussy or has a red lump on their thigh.


It is likely a virus if:

  • They have a runny nose or cough (rarely shot side effects).

  • The fever spikes 3 days or more after the appointment.


Keep Them Cool


If it is a vaccine reaction, focus on comfort. Heat makes it worse, so resist the urge to bundle them up. Strip them down to a diaper and a light onesie to let the heat escape. Keep the room at a comfortable 72°F - 75°F.


Focus on Hydration


Fever burns through fluids fast, so you need to be proactive. Offer breastmilk, formula, or water more frequently than usual to prevent dehydration.


When to Use Medicine


Try to treat the child rather than the number on the thermometer. If they are still playing and eating, you usually don't need to medicate them. Only reach for the medicine if they seem miserable.


Stick to Acetaminophen (Tylenol) for babies under 6 months. Once they are over 6 months, you can use Ibuprofen (Motrin/Advil) if you prefer.


You've Got This


A post-vaccine fever is a stressful rite of passage, but it means their body is building a shield against illness. Stay calm and give lots of extra cuddles.


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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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