In South Carolina, a measles outbreak broke out in the fall of 2025, with the number of cases rising to 185, of which 172 involved unvaccinated patients.[1] Later, the total number of infections rose to 646, including 88 new cases since the previous Friday.[2][3][4][7] Most of those infected were not vaccinated against measles, mumps and rubella (MMR).[1][2][3][4] The cases occurred at primary, secondary and higher schools as well as at two universities.[2][4] The outbreak is linked to a decline in vaccination coverage, which fell to 92.7 percent in the 2023-2024 school year.[1] In the US, 2,065 cases of measles were reported in 2025, the most since 1991.[1] Measles is highly contagious and can cause complications such as high fever, loss of hearing, vision, or encephalitis, with a death rate of two to three per 1,000 cases.[1] The US achieved measles-free status in 2000, but is now at risk of losing it.[7]