What Are the Normal Side Effects of Vaccines and When Should I Worry?
Normal reactions by vaccine, fever management at home, and warning signs that require a trip to KKH or NUH A&E.
Expected Reactions by Vaccine
Most vaccine reactions are mild and temporary. They are a sign that the immune system is responding and building protection. The absence of a reaction does not mean the vaccine did not work.
| Vaccine | Common Reactions | Timing | What to Do |
|---|---|---|---|
| BCG | Small red spot at injection site; develops into a small ulcer, then scar | 2 to 4 weeks after injection; scar takes 3 to 6 months to fully form | Normal; do not cover or treat. A scar is the expected outcome. |
| DTaP-IPV-Hib | Soreness and redness at injection site, mild fever, fussiness | 12 to 24 hours after injection | Cold compress, paracetamol for fever, extra comfort feeds |
| PCV13 | Injection site soreness, mild fever, irritability | Same day to 24 hours | Same as DTaP management |
| MMR | Fever (sometimes 39C), rash (measles-like), mild swollen glands | 5 to 12 days after injection (this delay is normal for live vaccines) | Manage fever with paracetamol; the rash is not infectious |
| Varicella | Mild rash (a few spots resembling chickenpox), low fever | 5 to 26 days after injection | Mild; cover spots if in contact with immunocompromised individuals |
| Rotavirus | Loose stools, mild fussiness | Within 1 week of dose | Normal; ensure good hydration |
Managing Fever After Vaccination
A low-grade fever (below 38.5C) after vaccination is normal and does not usually require medication. If your baby is uncomfortable or the fever is higher, paracetamol (Panadol) is the recommended choice.
- Use infant paracetamol at the dose appropriate for your baby's weight (always check the dosing chart)
- Do not use ibuprofen in babies under 6 months old
- Do not give aspirin to children
- Cool compresses on the forehead and skin-to-skin contact can help soothe an uncomfortable baby
- Ensure your baby is feeding well and staying hydrated during a fever
Pre-medicating debate: Some parents give paracetamol before vaccination to prevent fever. Current evidence does not support this practice: pre-medication may slightly reduce the immune response (lower antibody levels). Give paracetamol only if your baby has a fever or is clearly uncomfortable after vaccination.
Warning Signs: When to Seek Immediate Help
Serious adverse events after vaccination are rare. These signs require immediate medical attention. Go to KKH A&E or call 995:
Go to A&E Immediately If:
- High fever above 39.5C that does not come down with paracetamol
- Extensive rash all over the body appearing within minutes to hours of vaccination (possible allergic reaction)
- Difficulty breathing, wheezing, or swollen lips/tongue (possible anaphylaxis)
- Inconsolable high-pitched crying lasting more than 3 hours
- Febrile seizure (convulsion related to fever)
- Child becomes limp and unresponsive
- Severe swelling at the injection site beyond the immediate area
Febrile seizure: what to do. A febrile seizure is a convulsion caused by rapidly rising fever. If your child has a seizure: stay calm, lay them on their side, do not put anything in their mouth, do not restrain them, time the seizure, and call 995 if it lasts more than 5 minutes or if this is their first seizure. Febrile seizures are frightening but rarely cause lasting harm. Take the child to KKH or NUH for assessment afterwards.
Medical disclaimer: this article is for general informational purposes only. Always consult a healthcare professional for concerns about your child's health after vaccination. KKH's 24-hour A&E handles all paediatric emergencies: 6225-5554.