Vaccinations are one of the best methods of saving lives as they prevent diseases and illnesses. They will also prevent you from spreading disease to others, therefore reducing the risk of epidemics. The majority of vaccines are in the form of shots. While they are crucial for health, they can sometimes cause unpleasant reactions, including fever, redness, or swelling. In most cases, a fever after vaccination will be mild and last two days or less and it can be relieved with simple home care. In some cases, you will need medical attention.

Why Do Vaccines Cause Fever?

If you experience a fever after having a shot of vaccine, this is because vaccines are actually weakened versions of the virus. Your immune system will fight this weakened virus once it enters your body. A fever is simply a sign that the interactions of immune cells are creating antibodies. The fever helps to slow pathogens as they spread. Certain vaccines can cause fever, including:

• Vaccines for DTaP (diphtheria, tetanus, and acellular pertussis) or DPT (diphtheria, pertussis, and tetanus): Babies may experience a fever of 40°C or 104°F starting 2 or 3 hours after the shots. Children may also become fussy or experience sleepiness, poor appetite, swelling, or redness.
• Vaccines for MMR (measles, mumps, and rubella): Following this vaccine, the site of the shot may get slightly warm, hard, swollen, and/or red within the first one or two days. You may notice a fever as late as two weeks following the shot and a mild rash at up to three weeks.

When to See a Doctor

In the majority of cases, fever is completely normal and shouldn’t lead to a concern. After all, it helps your immune system to fight an infection. The fever may last for up to two days and this is normal. You should, however, get medical advice if the fever occurs in these circumstances:

• Your child is under 3 months old and the fever is 100.4°F (38°C) or higher.
• Your child’s fever lasts over 2 days.
• Your child has an earache, headache, or pain in his limbs or stomach.
• You notice vomiting or a rash.
• Swelling and/or redness at the injection site last over 48 hours.

The following circumstances are considered an emergency and require immediate medical attention or advice:

• The fever is above 104°F.
• The child appears very sick.
• There is a bulging fontanelle, which is the soft spot found on babies’ heads.
• Light hurts your child’s eyes.
• Your child has a stiff neck.
• Your child has a fit/convulsion that lasts over 5 minutes or has his/her first one.
• Your child has a seizure.
• You notice signs of an allergic reaction, including hives, wheezing, troubles in swallowing and breathing, paleness, weakness, hoarseness, dizziness, or a quick heart rate.
• You notice behavioral changes such as sleepiness, confusion, passing out, or being unresponsive.

How to Treat Fever After Vaccination at Home

As long as the fever doesn’t fit within any of the circumstances mentioned above, you will be able to take care of it with home remedies. Have your child rest and dress him/her in light clothing so he/she is comfortable. Give your baby a lot of fluids as well.

Depending on the extent of the fever, you can give your child ibuprofen or paracetamol to deal with discomfort from the fever. These medications can reduce the temperature, but won’t drop it to normal. Follow the label on the medication or your doctor’s instructions and never give your child these medicines for more than two days without consulting your doctor. Don’t give your child aspirin unless he/she is at least 20 years old.

How to Relieve Other Common Reactions After Vaccination

In addition to the possibility of fever after vaccination, there are other possible reactions. These can also typically be relieved at home and you will only need medical assistance in severe circumstances.

• Relieving Redness and Swelling: It is common for the injection site and surrounding area to look swollen or red. You can help this by applying a cool compress or wrapped ice pack for 10 to 20 minutes. You can also have ibuprofen or acetaminophen, provided you follow the instructions on the medication carefully.
• Relieving Poor Appetite and Fretfulness: Within several hours of vaccination, babies may be drowsy or fretful or even refuse to eat. It is best to plan on engaging in quiet activities at your house later in the day of the immunization. You should make sure your home is at a comfortable temperature to reduce fretfulness from overheating. Cuddle or hold your child as necessary.
• Relieving Skin Rash: Don’t worry if your child has a mild skin rash following the vaccination. This is common between 7 and 14 days after the immunizations for measles, mumps, rubella, and chickenpox. You don’t have to do anything for this rash. If it doesn't disappear within several days, consult your doctor.