The mother of a child with mumps tells the nurse that she does not understand how her son could have gotten mumps since he was immunized according to her physician's recommendations. What is the best response by the nurse.

Are you sure your child received an immunization for mumps.

I am wondering if your physician followed the immunization schedule correctly.

I am sure it must be frustrating. Where did you have the immunizations performed.

While immunizations are highly effective they aren't 100