The country's largest outbreak of measles cases since 1994 is going on in Ohio right now. Most of those are in the central Ohio area. In response to the measles outbreak, Gov. John Kasich issued an executive order authorizing pharmacists to administer the measles-mumps-rubella (MMR) vaccine to adults. State officials on Tuesday, however, are urging Ohio residents to call ahead before heading to pharmacies to get vaccinated.