My child developed a rash about a week after receiving the MMR vaccine. Could she have measles?

No, don't worry, your child doesn't have full-blown measles. She's having a common reaction to the live but weakened measles virus in the measles-mumps-rubella vaccine (MMR). Although the reaction looks like measles, your child isn't going to develop the disease itself with all its symptoms.

About 5 percent of children develop a rash after receiving the MMR vaccine, but the reaction is usually mild, transient, and doesn't require treatment. The rash can appear anytime between three days to 1 month  after the vaccination, although it usually shows up around the seventh to twelfth day following the vaccine. Children with a rash from the MMR vaccine are not contagious to others.

The rash typically starts as red dots on the chest and neck and fades away after a few days. In some cases it spreads to the rest of the body or the dots become raised bumps before fading away. Your child may have a  fever along with the rash that usually lasts 1 to 2 days, but may last up to five days.

When to worry

Some symptoms may actually indicate your child has another illness.

It's important to let your child's doctor know if:

• Your child has a high or prolonged fever or seems ill
• The rash spots are tiny or dark red and they don't blanch (turn white) when you apply pressure to them.

If your child develops symptoms immediately after receiving the MMR shot, however, she might be having an allergic reaction.

Call 911 immediately if your child has any of these signs right after the MMR shot:

• A severe rash or hives all over the body
• Difficulty breathing
• Swelling of the face, throat, lips
• Extreme weakness and can’t wake up.

These could indicate anaphylactic shock, a life-threatening condition. This type of reaction is exceedingly rare, but if it happens you need to call 911 and get your child to the hospital immediately.