A serum sickness-like reaction is when someone gets a fever, hives (raised red bumps on the skin), and arthritis after taking a medicine, having an infection, or, very rarely, getting a vaccine. The reaction can show up in days or weeks. The symptoms usually go away within a few days and do not cause any lasting problems. 

It is called a "serum sickness-like reaction" because it is similar to a reaction called serum sickness, but less severe.

• Give any medicines as prescribed by your health care provider.
• Let your child rest as needed.
• If your child still has a fever or joint pain, ask the health care provider if it's OK to give acetaminophen (Tylenol® or a store brand) or ibuprofen (Advil®, Motrin®, or a store brand). 
• If a medicine caused the reaction, make sure your child does not get that medicine again. Talk to your health care provider about other medicines that can be used.
• If a vaccine caused the reaction, make sure your child does not get that vaccine again.
• Tell all of your child's health care providers and the school nurse that your child has had a serum sickness-like reaction and what caused it.
• Ask your health care provider if your child should wear a medical alert bracelet.

Your child:

• feels worse
• still has symptoms after 2 weeks
• feels better, then gets sick again

What causes serum sickness-like reactions? Symptoms of serum sickness-like reactions happen when:

• The body's immune system, which fights infections and disease, reacts to something.
• A medicine damages cells or interacts with proteins in the body. 

How long do symptoms last? If a medicine caused the serum sickness-like reaction, symptoms often stop within a few days of stopping the medicine. If an infection or vaccine caused the reaction, it can take a few weeks for the symptoms to go away.