Last reviewed and updated by Dr Philippa Kaye: January 2024


Starting when you're baby is 8 week old, your GP will be using the NHS immunisation schedule to call your baby for a whole series of injections over the next year to protect against Meningitis B, diptheria, whooping cough, rotavirus – and more.

I know it feels like your baby is still so very little but it is important that they get their early-weeks immunisations to protect them against these potentially serious infections.

It can be really tough going through this with your baby. So, well done. And I don't mean to sound patronising: I mean it. As a mum myself, I know it isn’t fun but, as a doctor, I also know it is the best thing to do
Dr Philippa Kaye, expert family GP and mum of 3

Once your child has had a jab, you may find they have some after-effects which can last for a few days. (You can read how to deal with each of them further on in this article.) They may include:

  • fever
  • loss of appetite
  • grizzliness
  • abnormal crying
  • soreness/swelling around where they've had the injection
  • vomiting/diarrhoea

Not every baby will have these side effects but they aren't uncommon. They generally happen because the vaccine stimulates your baby's immune system – so that it can recognise that particular bacteria or virus again and help protect your baby against the disease in the future.

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But if your baby doesn't have any side effects, it doesn't mean that the immunisations aren't working. Side effects or not, the vaccines will be doing their job!

You're doing the right thing! It's not nice to give your baby something you know will make them cry and then may make them miserable for a day or so but you are protecting them from potentially fatal diseases. Vaccines work. They can save your child's life.
Dr Philippa Kaye, expert family GP and mum of 3

What are the key side effects after baby jabs – and how should I treat them?

I've listed the 6 key side affects – and how you should treat them – below. But, first and foremost, whatever side effects your baby is experiencing, if they are also not keeping down any fluids or if they are becoming floppy or unresponsive, seek urgent medical advice.

1. Fever

Fever (a high temperature, over 37.5°C) is probably the most common side effect of vaccinations.

For all of us, fever is a common and general response to an infection and while having injections doesn't infect your baby, the injection will stimulate your baby's immune system in the same way – to try and provoke immunity – and so a fever may develop.

Which vaccines are most likely to have fever as a side effect?

  • The Men B vaccine (given in 2 separate doses at 8 weeks and at 16 weeks) have a high chance of fever as a side effect. Because of this, it is now the recommended NHS protocol that you give your baby an age-appropriate dose of infant paracetamol after both doses of this vaccine.
    Studies show that giving paracetamol after the meningitis B vaccine reduces the risk of developing a fever without affecting the protective effects of the vaccine.¹
    The health professional who gives your baby their vaccine should give you information about this, including advice about how much paracetamol to give your baby and when.
  • Fever is also more common after the 2nd and 3rd dose of the 6 in 1 vaccine (at 12 weeks and 16 weeks).

What to do if your baby does develop a fever after their jabs

  • Keep them cool – so make sure they don't have too many layers of clothes/blankets
  • Give them plenty of fluids (breastfed babies may need extra feeds).
  • If your baby seems uncomfortable and unwell and is over 2 months old and weighs more than 4kg, you can give them an age-appropriate dose of infant paracetamol. This age/weight limit does not apply to the MenB vaccine at 8 weeks (see above).
  • As always, if you are concerned, please seek medical advice.
mum giving baby a reassuring cuddle

2. Loss of appetite

This can sometimes come when you have a fever, so don't be too surprised if your baby goes off their food for a while.

Which vaccines are most likely to have loss of appetite as a side effect?

  • This side effect is not associated with any vaccine in particular.

What to do if your baby has loss of appetite after their jabs

You do need to be careful that your baby doesn't get dehydrated. Signs of dehydration include:

  • Fewer wet nappies
  • A dry mouth

If you spot these, you should see your doctor.

More serious signs of dehydration include:

  • A sunken fontanelle (this is the 'soft spot' on top of your baby's head)
  • No tears on crying
  • No wet nappies for 6 hours
  • Rapid breathing
  • Drowsiness

If you spot these, you should see urgent medical help.

3. Grizzliness or more crying than usual

You might find that, after their injections, your baby's just not their usual happy self – even if they don't get a temperature. They also may not sleep well.

Which vaccines are most likely to have grizzliness/crying as a side effect?

  • This side effect is not associated with any vaccine in particular.

What to do if your baby has grizzliness/crying after their jabs

  • There's no specific treatment for this, apart from checking for fever and checking that they are drinking. But I recommend lots of cuddles and reassurance!

4. Soreness/swelling around where they've had the injection

Local reactions, such as redness, swelling or pain/discomfort, around the injection site are common.

Which vaccines are most likely to have soreness/swelling as a side effect?

  • This side effect is not associated with any vaccine in particular.

What to do if your baby has soreness/swelling after their jabs

  • If your baby is showing distress and seems to be in pain because of any swelling around where the injection was (usually arms or legs), you can help ease their discomfort with an age-appropriate dose of paracetamol-based medicine – provided they are over 2 months old and weigh more than 4kg. This age/weight limit does not apply to the MenB vaccine at 8 weeks (see the section on Fever above).
  • Don't panic: this is a very common side effect of an injection.
  • If the swelling gets worse or isn't going away, then do see your GP.

6. Vomiting/diarrhoea

If you find your baby is being sick or has more dirty nappies than usual after their injections, it could well be connected with their jabs.

Which vaccines are most likely to have vomiting/diarrhoea as a side effect?

  • In particular, the rotavirus vaccine (at 8 weeks and 12 weeks) can lead to mild diarrhoea.

What to do if your baby does develop a fever after their jabs

  • Ensure that your baby has enough fluids – so offer more milk.
  • Do see a doctor though if you're at all worried or the vomiting/diarrhoea symptoms seem to be getting worse, or if there are any signs your baby might be dehydrated (see the signs above in the section about Loss of appetite.)

What about the MMR and 'mini measles'?

The MMR vaccine (at 1 year and 3 years) can have some specific side effects.

These may include 'mini measles', which can occur 6 to 10 days after the vaccine, causing a fever, appetite loss and a measles-like rash.

Your child may also get 'mini mumps' 14 to 21 days after the vaccination, causing fever and swollen glands.

If your child gets either of these, they are not infectious. And they should recover quickly.


1. A phase 2 randomized controlled trial of a multicomponent meningococcal serogroup B vaccine. Prymula et al.Hum Vaccin Immunother. 2014;10(7):1993-2004. doi: 10.4161/hv.28666

Pics: Getty Images


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Dr Philippa Kaye works as a GP in both NHS and private practice. She attended Downing College, Cambridge, then took medical studies at Guy’s, King’s and St Thomas’s medical schools in London, training in paediatrics, gynaecology, care of the elderly, acute medicine, psychiatry and general practice.