Vaccination Day Is Here, but Baby Has a Fever… Now What?

Sam Ahn
Dec 15, 2025
3 min read

Written by Dr. Sam Ahn, MD (Family Medicine Specialist, Medical Contents Director of MoDoc AI) | 2025-12-15

You’ve had this appointment on the calendar for months. But of all days, you wake up this morning and your little one feels warm to the touch. Maybe there's a runny nose, too.

It’s that moment every parent dreads. Your heart sinks a little. “Do I need to cancel? If I give a shot to a sick baby, will it make them worse?” The anxiety starts to spiral.

Take a deep breath. This is actually one of the most common questions I hear in my clinic. As a doctor and a dad myself, I want to help ease your mind and give you a clear guide on what to do.

The Short Answer

You don’t necessarily need to cancel. Medically speaking, it is safe to vaccinate a child who has a runny nose or a mild fever. It won’t reduce the effectiveness of the vaccine.

Actually, the main reason we sometimes suggest rescheduling isn’t because it’s "dangerous." It’s because if your child spikes a fever later that night, we want to know if it's from the cold or from the shot. Vaccinating a sick child just makes it harder to tell the difference.

Bottom line: Don't auto-cancel. Call your pediatrician's office first to chat.

Why Do We Worry About "Sick Day" Shots?

Many parents worry that their child's immune system is already "busy" fighting off a cold virus, and adding a vaccine on top of that will cause an "overload."

However, according to the latest research, even with a mild fever, your child produces the same amount of antibodies (immunity) from the vaccine, and side effects do not increase.

What this means is 2 things:

You aren't "kicking them while they're down." Parents often fear that a shot will make a sick child feel ten times worse. Studies show that side effects (like a sore arm or fussiness) do not increase just because the child has a cold. You aren't adding extra danger or misery.
You aren't "wasting" the shot. You might worry that a busy immune system won't pay attention to the vaccine. The science says otherwise: even with a mild fever, your child’s body produces the exact same amount of protection (antibodies) as a healthy child. The vaccine works 100%.

Just a Cold, or Should We Wait?

Even though their immune system is tough, if your child is visibly miserable, there is no need to force the appointment today. Use this checklist to help you decide.

Good to Go (Mild Symptoms)

Temperature: Low-grade fever less than 101°F.
Mood: Playing well, happy, and eating normally.
Symptoms: Clear runny nose, mild cough.
Action: Call your doctor to confirm, but it's likely okay to go ahead.

Reschedule (Moderate to Severe)

Temperature: Fever of 102°F or higher, or if your child has chills.
Mood: Lethargic (acting droopy/tired), refusing to eat, or inconsolable crying.
Symptoms: Wheezing, trouble breathing, or signs of severe ear pain.
Action: It is best to postpone the shot until they feel better.

A Final Note

Worrying about your child? That just means you’re a great parent.

However, try not to miss an opportunity to protect your child from serious diseases over a simple sniffle. If your child's overall condition is decent, have a chat with your doctor—chances are, you can get that shot done and over with today!

Dr. Sam Ahn, MD

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.