I understand that ACIP changed its definition of evidence of immunity to measles, rubella, and mumps in 2013. Please explain.

In the 2013 revision of its MMR vaccine recommendations ACIP includes laboratory confirmation of disease as evidence of immunity for measles, mumps, and rubella. ACIP removed physician diagnosis of disease as evidence of immunity for measles and mumps. Physician diagnosis of disease had not previously been accepted as evidence of immunity for rubella. With the decrease in measles and mumps cases over the last 30 years, the validity of physician-diagnosed disease has become questionable. In addition, documenting history from physician records is not a practical option for most adults. The 2013 MMR ACIP recommendations are available at www.cdc.gov/mmwr/pdf/rr/rr6204.pdf.