Guidance

What to expect after vaccinations

Updated 24 December 2025

Applies to England

This guide tells you about the common side effects of vaccinations that might occur in babies and young children up to 5 years of age.

After a vaccination, your baby may cry for a little while, but that usually settles soon with a cuddle or a feed. Most babies don’t have any other reaction.

Reactions at the site of the injection

Some babies have some swelling, redness or a small hard lump where the injection was given and it may be sore to touch. This usually only lasts 2 to 3 days and doesn’t need any treatment.

Fevers

A fever is a temperature over 38°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, they may have a fever. You can check their temperature with a thermometer.

If your baby has a fever:

• don’t put them in a bath
• don’t sponge them down
• don’t put a fan on them

After vaccination with MenB

Fever can be expected after any vaccination, but is very common when the MenB vaccine is given with the other routine vaccines at 2 and 3 months. The fever shows the baby’s body is responding to the vaccine, although not getting a fever doesn’t mean it hasn’t worked. The level of fever depends on the individual child and does not indicate how well the vaccine has worked. Giving paracetamol will reduce the risk of fever, irritability and general discomfort (including pain at the site of the injection) after vaccination.

After each of the 2 month and 3 month vaccinations you will need to give your baby a total of 3 doses of paracetamol (2.5ml of infant paracetamol 120mg/5ml suspension) to prevent and treat any potential fever. You should give the first dose of paracetamol as soon as possible after your 2 month vaccination visit. You should then give the second dose 4 to 6 hours later and the third dose 4 to 6 hours after that. You will need to follow the same steps after your 3 month vaccinations. Your nurse will give you more information about paracetamol at your vaccination appointment and you may be given a leaflet to take away with you with written instructions.

Read more about Using paracetamol to prevent and treat fever after MenB vaccination on GOV.UK.

If you do not have any paracetamol liquid for infants at home you should get some in time for your first vaccination visit. It is widely available from pharmacies and supermarkets.

Remember! Never give medicines that contain aspirin to children under 16.

After vaccination with MMRV

MMRV protects against 4 infections (measles, mumps, rubella and chickenpox) and contains live, weakened viruses. The 4 viruses can cause reactions at different times after the injection. These mainly occur after the first dose.

The measles part of the vaccine starts to work 6 to 10 days after the immunisation. About 1 in 10 children may develop a fever and may be off their food. Some develop a measles-like rash which is not infectious.

The mumps and rubella parts of the vaccine start to work 2 to 3 weeks after the immunisation. A small number of children will have swelling of the face or pain in their joints. These are not infectious.

The chickenpox part of the vaccine starts to work from 3 to 4 weeks after immunisation. Some children will develop a few chickenpox-like spots at the site of the injection. The spots may contain infectious virus. As long as the spots are covered with clothing children can go to nursery as normal.

Any fever in a young child can sometimes lead to a seizure, also known as a fit. This is called a febrile convulsion. Usually, children recover quickly and there are no long-term consequences. Around 1 in 1000 children may have a fit caused by a fever after having their first dose of MMRV. This is usually in the second week after the vaccine.

Seek urgent medical advice if your child has a fit.

Call the doctor immediately if, at any time, your child has a temperature of 39-40°C or above.

If the surgery is closed and you can’t contact your doctor, trust your instincts and go to the nearest hospital with an emergency department. If, after having read this leaflet, you are still not happy with your baby’s reaction to any vaccination, speak to your practice nurse or GP. If you are worried about your child, trust your instincts. Speak to your doctor or call the NHS on 111.

Read more about MMRV and febrile convulsions on .GOV.UK.

Checking on vaccine safety

Before vaccines are introduced, they have to be licensed by the Medical and Healthcare products Regulatory Agency which assesses their safety and efficacy. Once they have been introduced into the programme, their safety continues to be constantly monitored so that any new side effects are quickly noticed and investigated. If you would like more information on the safety of vaccines visit www.mhra.gov.uk

More information

If you would like more information on the side effects of vaccines and vaccinations please see:

• A guide to immunisations up to 13 months of age
• www.nhs.uk/conditions/vaccinations