MenB vaccine side effects

The MenB vaccine has a good safety record. Many babies have no side effects at all, and 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 fever, or high temperature, so it's important to use paracetamol following vaccination to reduce the risk of fever.

In studies when the MenB was given to babies without paracetamol more than half of them developed fever. The fever peaks around six hours after vaccination but is nearly always gone within two days.

The fever shows that your baby is responding to the vaccine, although not getting a fever doesn't mean it hasn't worked.

Other common side effects of the MenB vaccine include:

  • pain, swelling or redness at the injection site
  • vomiting and/or diarrhoea
  • crying and irritability

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, and 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 for parents about paracetamol, which includes instructions on what dose to give your baby.

It's a good idea to have some liquid paracetamol at home before the two-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 being supplied with a sachet of infant paracetamol by the surgery or having liquid paracetamol that you've bought from a pharmacist.

Read this NHS leaflet to find out how to use paracetamol to prevent and treat fever 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 an anaphylactic reaction – a severe allergic reaction – within a few minutes of the vaccination. This can cause breathing difficulties and a person to 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 and, providing they receive treatment promptly, babies 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, though in general these are mild and short-lived. The vast majority of babies won't have any problems at all.

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

If your baby is unwell at any time after vaccination, or if you're concerned about their health, then trust your instincts and speak to your doctor or call NHS 111. Never give medicines that contain aspirin to a baby.

How to tell if your baby has a fever.

How to take your baby's temperature.

Get practical tips on how to cool down a baby with a fever.

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. Levels of disease and vaccine uptake are recorded by the Health Protection Agency, to measure the impact of vaccines on disease.

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 how to report a vaccine side effect.

Page last reviewed: 26/06/2015
Next review due: 26/06/2018