Is It Normal to Have a Fever After Vaccinations?
By Dr. Soo

Vaccinations are one of the greatest advancements in modern medicine. They have helped protect millions of children worldwide from dangerous infectious diseases such as measles, diphtheria, whooping cough, and many others. For parents, ensuring that their child is fully vaccinated is one of the most important steps in giving them a healthy start in life. However, it’s natural for parents to feel anxious when their child develops a fever after receiving a vaccination. Many wonder: “Is this normal? Should I be worried?” The good news is — in most cases, a mild fever after vaccination is completely normal and even a positive sign that your child’s immune system is responding appropriately.

Why Does Fever Happen After Vaccination?

To understand why fever occurs after vaccination, it’s important to know how vaccines work. Vaccines contain small, harmless components of viruses or bacteria — or sometimes just pieces of them — that train the immune system to recognize and fight these germs in the future. When your child’s body encounters the vaccine, their immune system treats it as an invader and starts building up defenses, producing antibodies to remember and fight the infection if it ever occurs later in life.

This immune response can cause temporary inflammation in the body, which may lead to mild side effects such as:

• Slight fever

• Fussiness or irritability

• Sleepiness or tiredness

• Mild swelling or redness at the injection site

Fever, in particular, happens because the immune system releases certain chemicals called cytokines. These chemicals act as messengers that tell the brain to raise the body’s temperature slightly, helping the immune system work more effectively. So, when your child develops a mild fever after a jab, it actually means the body is reacting and learning to protect itself — which is exactly what we want.

How Common Is Fever After Vaccination?

Mild fever after vaccination is very common among infants and children. Depending on the type of vaccine, studies show that around 10% to 30% of children may experience a mild fever within the first 24 hours after vaccination. The fever usually starts a few hours after the injection and lasts for one to two days.

For example:

• After the DTaP vaccine (which protects against diphtheria, tetanus, and pertussis), up to one in four children may experience a mild fever.

• The MMR vaccine (measles, mumps, rubella) can sometimes cause a fever about 5 to 12 days after vaccination.

• The influenza vaccine may cause mild fever or tiredness in a small number of children for a day or two.

 

These side effects are short-lived and much milder than the actual diseases that vaccines prevent.

When to Expect the Fever — And How Long It Lasts

The timing of post-vaccination fever depends on the type of vaccine given. Generally, there are two patterns:

1. Immediate reaction (within 24 hours)
   This is common with vaccines like DTaP, Hib, pneumococcal, or influenza. The fever usually appears within a few hours and lasts no longer than two days.

2. Delayed reaction (after 5–12 days)
   Some vaccines, such as the MMR vaccine, may trigger a fever several days later. This delayed fever corresponds to the body’s immune system continuing to build its defenses. It can last for up to three days, but usually resolves on its own.

In both cases, as long as your child remains alert, able to drink fluids, and doesn’t seem unusually unwell, there is usually no cause for concern.

What Parents Can Do at Home

Most mild fevers after vaccination can be managed at home with simple care. Here are some practical tips to help your child feel more comfortable:

1. Keep your child hydrated
   Offer frequent feeds if your baby is breastfed, or water for older children. Fluids help regulate body temperature and prevent dehydration.

2. Dress lightly
   Avoid heavy blankets or thick clothing. Dress your child in light, comfortable clothes to help the body release heat naturally.

3. Encourage rest
   Your child may be more tired or cranky than usual. Allow plenty of rest and quiet time.

4. Monitor the temperature
   Take your child’s temperature periodically. A mild fever (up to 38.5°C) is common and generally harmless.

5. Give fever medicine only if necessary
   Paracetamol can be given if your child is uncomfortable, in pain, or the fever is above 38.5°C. Always follow your doctor’s advice and use the correct dosage based on your child’s weight. Avoid giving medicine “just in case” if your child seems fine, as a mild fever helps the immune system work.

When to Seek Medical Attention

 

While a mild fever after vaccination is normal, there are times when you should consult your doctor. You should seek medical attention if:

• The fever lasts longer than 2–3 days

• Your child’s temperature is higher than 39°C

• Your child becomes unusually drowsy, irritable, or unresponsive

• There is persistent vomiting, refusal to feed, or difficulty breathing

• The swelling or redness at the injection site is worsening or spreading

• You notice a rash, seizures, or any unusual symptoms

These situations are uncommon but may require medical evaluation to rule out other causes or rare allergic reactions.

Rare Side Effects and Misconceptions

Parents sometimes worry about more serious reactions such as severe allergies or long-term effects. Severe allergic reactions (such as anaphylaxis) are extremely rare — occurring in less than one in a million doses — and clinics are equipped to handle such emergencies if they occur.

It’s also worth noting that vaccines do not cause conditions such as autism, chronic illnesses, or developmental delays. Decades of scientific research have proven vaccines to be safe and effective. Mild side effects like fever or soreness are normal signs that your child’s immune system is doing its job.

Supporting Your Child Through the Vaccination Process

Emotional support is just as important as physical care. For young children, vaccinations can be stressful experiences. Here are a few ways to make the process smoother:

• Stay calm and reassuring. Children pick up on parents’ emotions. A calm parent helps the child feel more secure.

• Distraction helps. Bring a toy, pacifier, or sing a song during the vaccination to ease anxiety.

• Comfort after the jab. Cuddles, breastfeeding, or gentle soothing after vaccination help your child recover faster.

• Praise your child. Encourage them by saying how brave they were — this builds a positive association for future visits.

The Takeaway

So, is it normal to have a fever after vaccination?
Yes — absolutely. A mild fever after vaccination is a common and expected response, showing that your child’s immune system is reacting as it should. Most children recover fully within a couple of days with simple home care. Remember to keep your child comfortable, hydrated, and monitor their symptoms. Seek medical help only if the fever is high, persistent, or accompanied by other concerning signs.

 Vaccines protect your child from serious, life-threatening diseases. The temporary discomfort of a mild fever is a small price to pay for long-term health and protection. With proper understanding and reassurance, you can help your child go through each vaccination confidently and safely.

Vaccination remains one of the most effective ways to safeguard your child’s health — and a little fever afterward is simply proof that their body is building strong, lasting immunity for the future.

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