Fever After Vaccination: What Parents Should Expect and When to Worry

A mild fever after the vaccination is one of the most common side effects of childhood immunisations. While it can feel worrying for parents, it is usually a normal sign that your baby’s immune system is responding and building protection.

In most cases, vaccine-related fever is mild, short-lived, and resolves within 24–48 hours without treatment.

This guide explains what is normal, what is not, and when you should seek medical advice.

What Causes Fever After Vaccination?

Vaccines work by training the immune system to recognise and fight harmful infections.

After vaccination, the immune system becomes temporarily activated. This immune response can cause mild symptoms such as the following:

• Low-grade fever
• Fussiness
• Sleepiness
• Reduced appetite

A fever after vaccination does not mean your baby is sick from the vaccine. It simply means the immune system is responding appropriately.

Is Fever After Vaccination Normal?

Yes—mild fever is a normal and expected side effect of many childhood vaccines.

Not every child develops a fever, and both responses are normal.

Other common side effects include:

• Redness or swelling at injection site
• Mild irritability
• Increased sleepiness
• Slight decrease in feeding

Which Vaccines Commonly Cause Fever?

Some vaccines are more likely to cause fever than others:

• DTaP (diphtheria, tetanus, pertussis)
• Pneumococcal vaccine (PCV)
• MMR (measles, mumps, rubella)
• MMRV vaccine
• Influenza vaccine
• Meningococcal vaccine

Fever is more common when multiple vaccines are given during the same visit.

When Does Fever Start After Vaccination?

Fever usually begins:

• Within 6–24 hours after vaccination
• Sometimes up to 48 hours later

Delayed fever (MMR vaccine)

Some vaccines, especially MMR, may cause fever 5–12 days later. This is expected.

How Long Does Fever Last After Vaccination?

Most vaccine-related fevers:

• Last 1–2 days
• Resolve on their own
• Do not require antibiotics

Seek medical advice if:

• Fever lasts more than 48–72 hours
• Fever goes away and returns
• Your child becomes more unwell

What Temperature Is a Fever?

A temperature of 38°C or higher is considered a fever.

Most post-vaccination fevers stay between 38°C and 39°C.

Fever After Vaccination by Age

Babies Under 3 Months

Any baby under 3 months with a fever of 38°C or higher must be assessed urgently, even after vaccination.

Babies 3–6 Months

Usually manageable at home. Monitor:

• Feeding
• Wet nappies
• Alertness
• Breathing

Seek help if the baby seems unwell.

Babies Older Than 6 Months

Care at home may include:

• Fluids
• Rest
• Light clothing
• Comfort measures

Paracetamol only if advised and correctly dosed.

Fever After Vaccination in South Africa (EPI Schedule)

In South Africa, babies receive routine immunisations under the Expanded Programme on Immunisation (EPI) at:

• 6 weeks
• 10 weeks
• 14 weeks
• 6 months
• 9 months
• 1 year
• 18 months

Because multiple vaccines are given at some of these visits, mild fever is common.

South African context:

• Fever after 6, 10, and 14-week vaccines is common
• The rotavirus vaccine may cause mild diarrhoea or irritability
• Combination vaccines may slightly increase fever risk

These reactions are expected and usually resolve within 1–2 days.

How to Comfort Your Baby at Home

• Offer frequent fluids (breast milk or formula)
• Dress the baby lightly
• Allow rest and sleep
• Monitor temperature with a digital thermometer
• Use medication only if advised

Should You Give Paracetamol Before Vaccination?

Routine use before vaccines is not recommended because it may reduce the immune response.

Treat only if symptoms develop.

Vaccine Fever vs Illness

Vaccine-related fever:

• Starts within 24–48 hours
• Mild
• Lasts 1–2 days
• No major additional symptoms

Possible illness:

• A fever lasts more than 3 days
• Cough, vomiting, or diarrhoea
• Baby is unusually sleepy or irritable
• Fever returns after improving

When Should Parents Worry?

Seek urgent medical help if your baby has:

• Fever above 40°C
• Difficulty breathing
• Seizures
• Refusal to feed
• Signs of dehydration
• Extreme sleepiness
• Allergic reaction (swelling, breathing difficulty)

Nurse’s Insight

As a primary health care nurse working with childhood immunisations, I often reassure parents that a mild fever after vaccination is expected.

Most babies recover within 24–48 hours with simple care such as fluids, comfort, and monitoring.

However, seek medical attention if:

• A young infant develops a fever
• The baby is difficult to wake
• Something does not feel right to the parent

Parental instinct is important.

Frequently Asked Questions

Is a fever after vaccination normal?

Yes, it is a normal immune response.

How long does it last?

Usually 1–2 days.

Can MMR cause delayed fever?

Yes, 5–12 days later.

Can a baby sleep with a fever?

Yes, but monitor regularly.

When should I worry?

If the fever is high or persistent, or if the baby is unwell.

The Bottom Line

Fever after vaccination is usually a normal and temporary immune response. It typically starts within a day, lasts 1–2 days, and resolves without complications.

If you found this post helpful, you might also like:

Baby Symptoms Guide: What’s Normal & When to Worry (A Nurse’s Guide for Parents)

Fever in Children: The “Wait or Worry” Checklist

Rising Temperature at Night: Should You Worry? A Nurse’s Guide

Child Fever: What Is Normal and What Isn’t

Baby Health Checklist: What’s Normal in the First 12 Months

Clinic or Hospital for a Sick Baby? Emergency Warning Signs Parents Should Know