Health officials are urging families across Fort Mill School District's 21 campuses to verify their children's vaccination records as South Carolina grapples with the second-highest measles case count in the nation.

The state has recorded 670 measles cases in 2026, trailing only Pennsylvania, according to the Centers for Disease Control and Prevention. No active cases remain in South Carolina as of Wednesday, Oct. 7, the South Carolina Department of Public Health (DPH) reported.

The district enrolled 18,229 students for the 2025–2026 school year, and state law requires a valid immunization certificate or approved exemption for every child in kindergarten through 12th grade.

South Carolina's cases stem largely from an Upstate outbreak that ran from October 2025 through March and totaled 997 infections across both years. DPH declared that outbreak over on April 27, after the last confirmed case was reported March 15. Spartanburg County accounted for 940 of those cases. York County recorded zero.

Of those infected in the Upstate outbreak, 932 were unvaccinated. Twenty had received one dose of the measles, mumps and rubella (MMR) vaccine, and 25 had received two doses. Children ages 5 to 17 made up the largest group at 639 cases, followed by 264 children under 5.

Nationally, the CDC counted 3,887 confirmed measles cases as of Oct. 1, with 95% tied to outbreaks. Pennsylvania leads the country with 1,004 cases, including five deaths, as first reported by ABC News.

Vaccination rates have declined. Nationwide, 92.4% of kindergartners received the MMR vaccine during the 2025–2026 school year, down from 95.2% in 2019–2020, according to the CDC. In South Carolina, 92.1% of kindergartners had two MMR doses during the 2023–2024 school year, the most recent state data available, down from 95% in 2019–2020.

Health experts consider 95% the threshold needed to keep measles from spreading through a community. Thirty-nine states fell below that mark in the 2025–2026 school year, according to a KFF analysis of CDC data.

The virus is highly contagious. Nine out of 10 unvaccinated people exposed to an infected person will catch it, according to the DPH. The virus can linger in the air for up to two hours after an infected person leaves a room.

Complications occur in as many as three out of 10 cases, most often in children under 5, adults over 20, pregnant women and people with weakened immune systems.

The CDC recommends two MMR doses: the first between 12 and 15 months of age, the second between ages 4 and 6. Two doses are 97% effective at preventing infection.

South Carolina permits medical and religious exemptions from the vaccination requirement. Children with exemptions may be excluded from school during an outbreak of a vaccine-preventable disease, according to the DPH.

Fort Mill School District requires families to submit immunization records to the school nurse within 30 days of the first day of school, according to the district's enrollment page. In an April 27 statement marking the end of the Upstate outbreak, DPH said vaccination remains the best way to prevent measles and that vaccines are available at primary care offices, pharmacies and public health departments.

Families who received immunizations from South Carolina providers can check records through the DPH's SIMON portal at simonportal.dph.sc.gov. The York County Health Department, at 1070 Heckle Blvd. in Rock Hill, offers immunizations and can be reached at (803) 909-7300.