Why might my baby have a fever after injections?

Baby vaccines are an important milestone in the first year, but why can injections cause a fever? And when should you visit a doctor?

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Fever after baby inoculations can be relatively common, and with vaccinations at 8 weeks, 12 weeks, 16 weeks and a year in the UK, it can feel like a treadmill of trips to the GP.

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While baby vaccines can be a worry, especially if your child has a fever after their inoculation, there are ways to help them feel better and we share the most up-to-date guidance and in-depth advice from a doctor.

Why might my baby have a fever after injections?

If your baby has a fever after their jabs, you’re not alone, as many of the common vaccines can cause a high temperature as a side effect.

MFM’s consultant GP Dr Philippa Kaye explains: “A fever is an immune system response to fight an infection.

“Although there is no infection after a vaccination the body’s immune system is stimulated in the same way to try and provoke immunity and so a fever may develop.”

Read more on what temperature is in a fever in babies and toddlers, and when to call a doctor.

Can my baby have immunisations if they already have a fever?

If your child has a fever or is unwell in themselves then you should postpone vaccinations until they’re better, says Dr Kaye.

Which vaccinations cause a fever?

Your baby is going to have a number of different immunisations between the age of 8 weeks and a year – and some can be more likely to cause a fever than others.

Dr Kaye says: “Fevers are more likely after the Meningitis B vaccine – given at 8 weeks, 16 weeks and one year of age.”

All babies will react differently to their jabs, as mum MrsCoco found for her baby’s injections. Writing on our forum, she said: “After 8wk ones O was fine….. in fact he was the incredible sleeping baby….slept most of the day and happy when awake. Twelve and 16 weeks were another matter entirely for us though with rattiness, crying and temp for a few days after.”

The vaccination schedule for the first year in the UK is:

8 weeks

  • 6-in-1 vaccine for all babies born on or after 1 August 2017 (diphtheria, tetanus, whooping cough, polio, Hib/Haemophilus influenzae type b and hepatitis B)
  • Pneumococcal or pneumo jab (PCV)
  • Rotavirus vaccine
  • Meningitis B vaccine

12 weeks

  • 6-in-1 vaccine for all babies born on or after 1 August 2017 (diphtheria, tetanus, whooping cough, polio, Hib/Haemophilus influenzae type b and hepatitis B
  • Rotavirus vaccine

16 weeks

  • 6-in-1 vaccine for all babies born on or after 1 August 2017 (diphtheria, tetanus, whooping cough, polio, Hib/Haemophilus influenzae type b and hepatitis B
  • Pneumococcal or pneumo jab (PCV)
  • Meningitis B vaccine

1 year

  • Pneumococcal or pneumo jab (PCV)
  • Meningitis B vaccine
  • Hib/Meningitis C vaccine
  • Measles, mumps and rubella vaccine (MMR)

Parents should also look at the NHS website for vaccinations after one year. 

Different vaccinations can cause a variety of side effects, with many babies given the Meningitis B vaccine alongside their other routine vaccinations at 8 and 16 weeks likely to develop fever within 24 hours of vaccination, according to the NHS. 

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The NHS also reports at least 1 in 10 babies get a fever of 38C or above after the Hib/Men C immunisation, while the pneumococcal vaccine can also sometimes cause a fever.

Fever after injections is a common side effect for up to 1 in 10 babies having the 6-in-1 vaccine, according to the NHS, it is rare for a child to get a high fever above 39.5C, which has been reported in fewer than 1 in 10,000 babies.

And according to the NHS, some little ones may develop a very mild form of measles – including a rash, high temperature and feeling of being unwell – about a week after the MMR jab.

“The MMR vaccine, like any vaccine, can also produce a temperature but this one tends to appear much later,” says Dr Kaye.

According to the NHS website, about 3-4 weeks after having the MMR jab 1 in 50 develop a mild form of mumps. 

Mum Ninabeanie shared her daughter Molly’s reaction to the MMR jab on our forum: “Her temp raised high and she vomited several times but it was under control very quick with meds and she was back to her bouncy self the next day.”

Does a fever mean my baby’s injections haven’t worked?

Luckily, having a fever definitely doesn’t mean the injections haven’t worked, so there’s no need to worry.

As a fever is the immune system’s response to fight an infection, “actually it means things are working!”, says Dr Kaye.

“Though not having a fever does not mean that it isn’t working and how high the temperature of the fever is doesn’t give an indication of how well things are working!” she adds.

Why is my baby cranky after injections?

It’s not unusual for babies to get cranky after injections – after all, none of us particularly enjoys getting a jab!

As well as the immediate injection, vaccinations can cause some localised soreness for a couple of days, irritability, as well as sparking a fever as the immunisation gets to work.

“Some children may develop a fever after their immunisations, and indeed it can be worth checking if they are miserable and irritable in the day or so after the injection,” explains Dr Kaye. 

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What should I do if my baby seems unwell after vaccinations?

A good start is to take your baby’s temperature with a reliable and accurate thermometer, to check their temperature during a fever. (Accurate within ±0.2° Celsius with correct usages. Environmental factors & child’s position may result in greater variance in accuracy). 

The Nurofen For Children FeverSmart™ Temperature Monitor can give reassuring peace of mind, as it has a patch that sticks gently under your baby’s armpit and connects to your smart phone to give continuous temperature readings, and even alerts you (with a beep and visual cues) if your little one’s temperature becomes too high.

“If your child does have a fever but is happy in themselves, alert and feeding as normal you do not need to treat them, but if they are miserable then do!” says Dr Kaye.

“Hot and happy doesn’t need treatment but hot and miserable does. You can use paracetamol or ibuprofen but also give plenty of fluids – a breastfed baby may need or want to feed more often.”

How long will a fever last after injections?

Thankfully, if your baby does get a fever after vaccinations, it shouldn’t last longer than a day or two.

“Side effects tend to be relatively short lived – a couple of days,” reassures Dr Kaye. “The fever tends to appear within about 6 hours and disappear within 2 days.”

How can I make my baby feel better when they have a fever after vaccinations? 

Because a fever can be common after jabs, especially the Meningitis B vaccination, it is worth thinking about giving liquid paracetamol, which can be given from 2 months.

“Parents are recommended to give liquid paracetamol, generally as soon as possible after the vaccine and then a dose afterwards with a 4-6 hour gap in between,” explains Dr Kaye.

“If your baby was born prematurely please check with your nurse or doctor regarding the dosage.  “Without the paracetamol over half of babies will develop a fever with the Meningitis B vaccine and paracetamol decreases this by about half.”

It’s a good idea to make sure your baby isn’t overdressed in too many layers, and look out for signs of dehydration like fewer wet nappies, a dry mouth and sunken eyes.

Encourage your baby to drink lots, and check on them while they’re asleep or during the night.

It’s important to remember not to give paracetamol to babies under 2 months, and not to give ibuprofen to babies under 3 months or weighing less than 5kg, or to those with asthma.

When should I go back to the doctor?

“When to return to the doctor depends on how unwell they may be,” explains Dr Kaye. “If your baby is feeding and happy in themselves despite a fever then you can just monitor them.

“But if they are not feeding and aren’t producing wet nappies, then seek medical advice and get medical help urgently if they are listless and lethargic or floppy. 

“As always if you are concerned ask for help from your GP.” 

*Dr Kaye does not endorse amy medicinal products or brands.

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