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MenB vaccine side effects

The MenB vaccine has a good safety record. Many babies have no side effects at all. In those that do, any side effects tend to be mild and short-lived.

Common side effects of the MenB vaccine

The most common side effect seen with the MenB vaccine when it's given alongside other vaccinations is a high temperature (fever).

It's important to use paracetamol after vaccination to reduce the risk of a fever.

Studies found that when the MenB was given to babies without paracetamol, more than half of them developed fever.

The fever peaks around 6 hours after vaccination, but is nearly always gone within 2 days.

The fever shows that your baby is responding to the vaccine, although not getting a fever does not mean it has not worked.

Other common side effects of the MenB vaccine in babies and young children include:

  • loss of appetite
  • sleepiness
  • unusual crying and irritability
  • vomiting and/or diarrhoea

The most common side effect in older children, teenagers and adults is pain, swelling or redness at the injection site.

MenB vaccine and paracetamol

It's recommended that you give your baby liquid paracetamol to reduce the risk of fever after vaccination. 

Giving paracetamol reduces the chances of your baby getting fever by more than a half. Nearly all these fevers are mild.

Your nurse will give you more information about paracetamol at your vaccination appointment.

You'll also be given a leaflet which includes instructions on what dose to give your baby. The leaflet for parents about paracetamol is available on GOV.UK.

It's a good idea to have some liquid paracetamol at home before the 2-month vaccination visit. You can buy it from your local pharmacy or supermarket.

Premature babies, MenB vaccine and paracetamol

If your baby was born before 32 weeks, they should have paracetamol prescribed for them according to their weight, rather than having a sachet of infant paracetamol supplied by the surgery or liquid paracetamol you've bought from a pharmacy.

This leaflet on GOV.UK explains how to use paracetamol to prevent and treat a high temperature after MenB vaccination.

Rare side effects of the MenB vaccine

Allergic reaction

In rare cases, babies can have an allergic reaction to the MenB vaccine soon after the injection. This may take the form of a rash or itching that affects part or all of their body.

In very rare cases, they may have a severe allergic reaction (anaphylaxis) within a few minutes of the vaccination. This can cause breathing difficulties and collapse.

It's very alarming at the time, but the doctor or nurse giving the vaccine will have been trained in how to treat these reactions.

Provided the baby receives treatment promptly, they should make a complete recovery.

You can read more about the side effects of the MenB vaccine in the patient information leaflet for Bexsero (PDF, 226KB).

What to do if your baby is unwell after the MenB vaccine

As with all vaccines, a few babies will have side effects, such as looking red or flushed, crying, feeling a bit irritable and so on, although in general these are mild and short-lived.

The majority of babies will not have any problems at all.

Follow the advice of your nurse about how to use liquid paracetamol to prevent fever after vaccination.

If your baby is unwell at any time after vaccination or you're concerned about their health, trust your instincts and speak to your doctor or call NHS 111.

Never give medicines that contain aspirin to a baby.

Read more about a high temperature (fever) in children.

Find out how to take your baby's temperature

Monitoring the safety of the MenB vaccine

In the UK, the safety of vaccines is monitored through the Yellow Card Scheme by the Medicines and Healthcare products Regulatory Agency and the Committee on Safety of Medicines.

Most reactions to vaccines reported through the Yellow Card Scheme have been minor, such as rashes, fever, vomiting, and redness and swelling where the injection was given.

Find out why vaccination is safe and important

Page last reviewed: 6 September 2021
Next review due: 6 September 2024