Vaccine Side Effects in Children: Common Reactions and Urgent Warning Signs

Mild fever, soreness, redness, tiredness, or fussiness can occur after vaccination. What matters is how severe the reaction is, how quickly it progresses, and whether breathing, alertness, hydration, or circulation is affected.

Common short-term reactions

• Pain, redness, or mild swelling at the injection site
• Mild fever
• Tiredness or irritability
• Reduced appetite for a short period
• Mild body aches

Seek emergency care immediately

• Difficulty breathing, noisy breathing, or throat tightness
• Swelling of the face, tongue, or lips
• Collapse, severe weakness, poor responsiveness, or seizure
• A rapidly spreading rash with breathing or circulation symptoms
• Any rapidly worsening reaction

Call the pediatrician

• Fever is persistent, unusually high, or the child looks very unwell.
• Swelling or pain is severe or continues to worsen.
• The child is not drinking, urinating less, or is unusually sleepy.
• You are unsure whether the symptoms are expected.

What to record

Write down the vaccine, time given, time symptoms started, temperature, medicines given, and photos of any rash or swelling. Bring the vaccine record to follow-up.

Before the next dose

Tell the doctor about any previous reaction. Do not assume every reaction means future vaccines are unsafe. The next plan depends on the type and severity of the reaction.

Book a post-vaccine review or open the vaccine planner.

Source

World Health Organization vaccine safety resources

Medically reviewed by Dr. Justin Ong Ho. Last reviewed August 1, 2026.