Possible reactions to immunisations

Modern vaccines have far fewer side effects than in the past and most children do not have any reactions to them.

This information tells you about the occasional possible side effects of immunisations that might occur in babies and young children up to five years of age.

Only use this information as a guide. Contact our rooms if you are concerned about your child.

Common Side Effects

After immunisations given to children under 5 years of age the most common side effects are at the site where the injection was given, these include:

  • swelling
  • redness
  • a small hard lump

These symptoms usually pass within a couple of days and you don’t need to do anything about them. Sometimes your child may develop a fever. It is normal for your baby to be upset for up to 48 hours after having the injection. To help comfort your baby, you can:

  • give them a cuddle
  • offer them extra drinks
  • take them for a walk in the fresh air.

If the injection site is flushed, put a clean cold cloth to the area for about 5 to 10 minutes – this may help to soothe your baby.
After reading this guide, if you are still not happy with your baby’s reaction to any immunisation, speak to your practice nurse or doctor.

After immunisation with MMR

MMR is made up of three different vaccines (measles, mumps and rubella) which can cause reactions at different times after the injection.

Side effects of MMR may include:

  • After 6-10 days the measles vaccine starts to work and may cause a fever, a measles-like rash and a loss of appetite.
  • Around 2-3 weeks after the injection the mumps vaccine may cause mumps-like symptoms (fever and swollen glands) in some children.
  • Most commonly around 12-14 days after the injection the rubella vaccine may cause a brief rash and possibility a slightly raised temperature, and on rare occasions a rash may also occur up to 6 weeks later.
How to treat a fever

A fever is a body temperature over 37.5°C. Fevers are quite common in young children, but are usually mild. If your child’s face feels hot to the touch and they look red or flushed, he or she may have a fever. You can check their temperature with a thermometer.

Keep your child cool by:

  • making sure they don’t have too many layers of clothes or blankets on (remove clothes)
  • turning down the house heating
  • giving them plenty of cool drinks (if you are breastfeeding, your child may feed more frequently)

You don’t need to put them in a bath, sponge them down or put a fan on them. There is no evidence that this will lower your child’s fever.

As fevers are usually mild, you only need to give a dose of infant paracetamol if your child appears uncomfortable or unwell.

For further information on possible side effects of vaccines see:
https://www.cdc.gov/vaccines/vac-gen/side-effects.htm