Colorado health officials have warned that thousands of people could have been exposed to measles after an infectious traveler passed through Denver International Airport on 12 August and a second case was confirmed in Mesa County. The Colorado Department of Public Health and Environment said anyone who was near Gate C51 upon arrival and the connecting flight at Gate C50 on Concourse C may have been exposed. Potentially affected individuals—particularly those without measles-mumps-rubella (MMR) vaccination—should monitor for fever, cough, runny nose and rash through 5 September and avoid large gatherings if symptoms develop. The newly identified patient is an adult Mesa County resident whose vaccination status is unknown and who may share an exposure source with the county’s first case reported last week, indicating possible undetected community spread around Grand Junction. Colorado has now recorded measles infections in eight counties this year, its heaviest caseload since 1995. State data show 92 percent of kindergartners received the two-dose MMR series in the 2024-25 school year, slightly below last year’s level. CDPHE urged travelers to confirm their immunizations and noted that post-exposure vaccination within 72 hours can prevent illness.