Nearly all measles cases have been in people who had not received the highly effective measles-mumps-rubella (MMR) vaccine or whose vaccination status is unknown. - Jayla Whitfield-Anderson/Reuters

Thanks to widespread vaccination, measles had been considered “eliminated” as a continually transmitting illness in the United States since 2000 – but not anymore.

An independent commission of experts that reports to the director of the Pan American Health Organization determined that the US no longer qualified as having eliminated measles, a source close to the process told CNN on Fri...