vaccine side effect with fever

Overview

A fever is a temporary rise in body temperature. After a vaccine, a low-grade fever is a normal sign that your immune system is responding and learning to fight the infection.

Yes. Many people, especially children, develop a mild fever within 24 hours after certain vaccines.

Anyone can have a fever after vaccination. It is most common in children under 6 and after vaccines like the flu, pneumococcal, or combination childhood vaccines.

Symptoms

Common symptoms

• Temperature between 37.5°C and 38.5°C (99.5°F to 101.3°F)
• Chills or feeling cold
• Tiredness or sleepiness
• Mild headache
• Muscle aches
• Pain, redness, or swelling where the shot was given
• Loss of appetite

Symptoms in children

• Same temperature range as above
• Fussiness or crying more than usual
• Being sleepier than normal
• Not feeding or eating as well
• Mild skin rash (in some cases)

Symptoms in older adults

• Fever may be lower than in younger people, but still makes you feel unwell
• Tiredness and weakness
• Aching muscles
• Confusion or increased confusion (seek medical advice if this happens)

Causes

Main causes

• Your immune system's normal response to the vaccine
• The vaccine helping your body create immunity without causing the disease

Risk factors

• Being a child or infant
• Receiving certain vaccines that are more likely to cause fever
• Having had a fever after a vaccine before
• Getting multiple vaccines at the same time

When to see a doctor

See a doctor urgently if:

• Fever is higher than 40°C (104°F) or keeps climbing
• You or your child look or act very ill
• The area around the injection becomes very red, hot, or painful
• You are worried because the fever is not going away after 3 days

Book a routine appointment if:

• You are unsure or just want reassurance from a pharmacist or nurse
• You have a health condition such as a weakened immune system and want advice
• Your child is under 3 months and has any fever

Diagnosis

In most cases, you don't need a diagnosis for a post-vaccine fever. A healthcare provider can confirm the cause by asking about your symptoms and when you received the vaccine.

Tests that may be done

• A thermometer reading to confirm the fever
• A physical check-up to rule out other causes if the fever is high or lasts longer than expected
• Sometimes urine or blood tests if an infection is suspected

What to expect at your appointment

If you see a doctor about a post-vaccine fever, they will likely look at how you feel overall and ask how long it's been since the shot. You can expect a simple exam and advice on comfort measures.

Treatment

Treatment focuses on comfort, not on 'curing' the fever, because the fever itself is a normal immune response. Most people recover quickly with rest and fluids.

Self-care at home

• Drink plenty of water, broth, or clear fluids to stay hydrated
• Rest and let your body recover
• Keep your room at a comfortable temperature
• Use a cool, damp cloth on your forehead or the back of your neck
• Dress in light, breathable clothing
• For children, encourage extra feeding or breastfeeding

Medical treatments

Your doctor or pharmacist can suggest a fever-reducing medicine if the fever is making you very uncomfortable. They will tell you the right amount for your age and weight. Never give medication without medical advice.

Living with this condition

While the fever lasts, take things easy. You do not need to stay in bed, but listen to your body. For children, it's fine to let them rest and return to normal activities when they feel better.

Lifestyle tips

• Avoid strenuous exercise until the fever goes
• Get enough sleep to help your immune system
• Don't pile on heavy blankets if you have chills — use layers you can remove
• For older adults, keep moving gently around the house to prevent stiffness

Diet and exercise

Eat light meals if you feel hungry, but focus on fluids first. You don't need to force food. Gentle movement is okay, but wait until the fever has been gone for 24 hours before returning to intensive exercise.

Mental health and emotional wellbeing

Feeling unwell can make you feel low or anxious. This is normal and usually short-lived. Remind yourself that the fever is a sign of protection, not sickness from the vaccine itself.

Prevention

You cannot completely prevent a fever after a vaccine — it's your immune system's natural response. But you can reduce discomfort by staying hydrated and dressing comfortably before and after your shot.

Vaccines

Vaccines are the safest way to build immunity. The temporary fever they may cause is far less serious than the complications of the diseases they prevent.

Complications

If left untreated

• In nearly all cases, there are no complications. The fever settles on its own.
• Rarely, a very high fever in young children can cause a febrile seizure, which is scary but usually not harmful. Seek medical help if a seizure happens.

Long-term outlook

The outlook is excellent. A post-vaccine fever is a short-lived immune response that usually resolves within 48 hours. Your body is doing exactly what it needs to do to protect you.

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