How to Treat Fevers and Other Vaccine Reactions

Ensuring children receive timely vaccinations is critical for their health. While concerns may arise—especially with multiple doses—most children experience mild or no reactions. Post-vaccination fever is common; severe reactions are very rare. Monitoring your child afterward is wise.

Below are vaccine reaction symptoms to watch for and how to respond.

• Vaccines are very safe. Most children have mild or no side effects. Those with reactions may experience injection site pain, low fever, fussiness, chills, or muscle aches.
• Fortunately, severe reactions are rare. Watch for serious symptoms like seizures, high fever, or a rash of small red/purple spots or bruises. Call 911 immediately for signs of severe allergic reactions: hives, difficulty breathing, pale skin, or loss of consciousness.
• For low post-vaccination fever, give ibuprofen (for children ≥6 months) or acetaminophen (for ≥3 months). Consult a doctor if unsure.
• While severe reactions sound alarming, most children have mild or no symptoms. Vaccines are safe, effective, and protect against potentially severe diseases.

Managing Fever and Mild Vaccine Reactions

Many children have no side effects; those who do often have mild symptoms. Common reactions include:

• Injection site pain, redness, or swelling
• Low fever lasting 1–2 days
• Chills
• Headache or muscle aches
• Fussiness

These resolve on their own. For discomfort, give ibuprofen (≥6 months) or acetaminophen (≥3 months). Consult a doctor with concerns. Certain vaccines may cause specific reactions: MMR can trigger fever and rash 7–10 days post-injection; DTaP rarely causes brief crying or fussiness. Despite rare side effects, the risk of long-term issues from vaccine-preventable diseases far outweighs those from vaccines.

“While rare side effects exist, infants are more likely to develop long-term consequences from vaccine-preventable illnesses than from vaccines themselves,” notes Dr. Dezure.

When to Contact a Doctor

Most reactions are mild, but call a doctor for:

• Bleeding issues: Rarely, autoimmune reactions may reduce platelets, causing easy bruising, bleeding gums, blood in stool/urine, or prolonged bleeding. A rash of small red/purple spots may appear. Contact a doctor immediately.
• Seizures or high fever (≥104°F): If unable to reach a doctor, go to a pediatric emergency room. Inform providers of vaccines received, timing, and symptoms.
• Rash, vomiting, swollen lymph nodes, or prolonged crying: These are unlikely to signal serious issues but warrant a call if concerning.

When to Call 911

Some reactions are emergencies. Call 911 for:

• Hives
• Difficulty breathing
• Pale skin or weakness
• Loss of consciousness

These may indicate anaphylaxis, a life-threatening allergic reaction. Though extremely rare (1 in 1 million, per the CDC), monitoring post-vaccination is important.

U.S. healthcare providers must report suspected severe reactions to the Vaccine Adverse Event Reporting System (VAERS). Dr. Dezure notes VAERS should reassure parents: doctors prioritize vaccine safety, and data—including parent reports—confirms vaccines are safe and effective for most children.

While vaccines carry rare but severe risks, they are vital for preventing serious diseases like measles, which can harm or kill children. Most children experience only mild, short-lived symptoms—or none at all.