What are the side effects of baby vaccinations?

By Dr Mitsu Shah, Paediatric GP at Kidswell Health

Vaccinations are one of the most effective ways to protect your baby from life-threatening illnesses such as meningitis, measles, and whooping cough. In the UK, the NHS recommends a series of vaccinations starting when your baby is just 8 weeks old. To find out more about the vaccination schedule for babies head to our blog here.

As a parent, it’s normal to feel concerned about how your baby will react. Most babies cope very well with vaccinations, but some will experience temporary side effects. Understanding what to expect can help you feel prepared and reassured.

Why do baby vaccinations cause side effects?

Side effects happen because vaccines stimulate your baby’s immune system to build protection. This immune response can sometimes cause symptoms such as fever, fussiness, or a sore arm. These are short-term signs that your baby’s body is learning to fight the disease.

Common side effects of baby vaccinations

Most side effects are mild and only last a day or two. The most common ones include:

• Soreness, redness, or swelling at the injection site: a small lump or tenderness is common, especially after jabs in the thigh.
  
• Mild fever: particularly after the MenB vaccine, given at 8 and 16 weeks. NHS guidance recommends giving infant paracetamol after this vaccine.
  
• Fussiness or irritability: your baby may be unsettled or cry more than usual.
  
• Tiredness or sleepiness: some babies nap more after their jabs.
  
• Reduced appetite: your baby may feed a little less for a day or so.
  

Less common side effects

Occasionally, babies may experience:

• A higher temperature (above 39°C)
  
• Diarrhoea or vomiting (sometimes linked to the oral rotavirus vaccine)
  
• A temporary rash (for example, a mild rash after the MMR vaccine)
  
• Swollen glands in the neck or groin

These are still usually short-lived and not harmful.

Rare side effects

Serious reactions to baby vaccinations are extremely rare. However, you should seek urgent medical advice if your baby:

• Has a fever above 39°C that does not settle with paracetamol
  
• Experiences a seizure (fit)
  
• Cries inconsolably for more than 3 hours
  
• Develops breathing difficulties, wheezing, or a hoarse cry
  
• Shows signs of a severe allergic reaction (very rare) such as swelling of the face, lips, or tongue, or sudden difficulty breathing
  

Call 999 or go to A&E if you think your baby is having a severe reaction.

How to manage side effects at home

• Use infant paracetamol if advised (especially after the MenB vaccine)
  
• Offer frequent feeds: small amounts of milk can help if appetite is low
  
• Keep your baby cool if they have a mild fever, but don’t overdress them
  
• Comfort and cuddle: holding your baby close helps them settle more quickly
  
• Monitor symptoms: most side effects should ease within 48 hours
  

Reassurance for parents

It’s natural to worry when your baby feels unwell after a vaccination, but remember: these side effects are short-term and far less serious than the illnesses the vaccines protect against.

For more detail on when each vaccine is given, see our blog on the updated NHS baby vaccination schedule.

Plus, read our blog on how to prepare for your baby’s first vaccination here.

Baby vaccinations are safe, effective, and protect against serious diseases. While mild side effects are common, serious reactions are rare. If you’re unsure or worried about your baby’s symptoms, always contact your GP or NHS 111 for advice.

At Kidswell Health, our paediatric team is here to support parents through every stage of their baby’s health journey, from routine check-ups and routine vaccinations to personalised vaccination advice.

Book a vaccination or a consultation with our paediatric specialists

FAQs about the side effects of baby vaccinations

What are the most common side effects of baby vaccinations?
The most common side effects are a sore or swollen injection site, mild fever (especially after the MenB vaccine), fussiness, tiredness, and reduced appetite. These usually last only a day or two.

Do babies feel pain during vaccinations?
Yes, babies may cry briefly when the needle goes in, as they feel a momentary sting or discomfort. The good news is that the pain is very short-lived, and most babies settle quickly with cuddles, breastfeeding, or a bottle straight after.

Is it normal for my baby to have a fever after vaccinations?
Yes. A mild fever is common, especially after the MenB vaccine given at 8 and 16 weeks. Infant paracetamol is recommended by the NHS to reduce discomfort and lower temperature.

How long do side effects from baby vaccinations last?
Most side effects settle within 24–48 hours. Some, such as mild swelling at the injection site, can last up to a week but should not cause ongoing problems.

Can vaccinations cause serious side effects?
Serious side effects, such as severe allergic reactions, are extremely rare. The benefits of protecting your baby against serious illnesses far outweigh the small risks of side effects.

What should I do if my baby won’t stop crying after their jabs?
Crying for a short while is normal, but if your baby cries inconsolably for more than 3 hours, or you’re worried, seek medical advice from your GP or NHS 111.

Can my baby have vaccinations if they were premature?
Yes. Premature babies are often at greater risk of infections, so it’s important they are vaccinated according to the same schedule as other babies, starting at 8 weeks (or 8 weeks corrected age if advised by your doctor).

Do you provide routine vaccinations at Kidswell Health?
Yes. At Kidswell Health, our paediatric team offers routine vaccinations alongside check-ups and expert advice. We provide a calm, child-friendly environment to make the process as stress-free as possible for both you and your baby.