A measles outbreak in South Carolina has exploded to 434 cases, doubling in just one week. Health officials report 409 people are in quarantine after exposure. The surge includes 124 new cases identified since last Friday, overwhelming containment efforts in the Spartanburg area.

The highly infectious virus has prompted health officials to activate a mobile unit offering free MMR vaccinations. However, authorities admit they are losing the ability to trace infections. One contagious person recently visited the South Carolina State Museum, putting unvaccinated visitors at risk.

This three-month-old outbreak is on track to rival Texas’s massive 2024 event. With the US recording its highest case numbers since 1991, the failure to curb transmission underscores the vulnerability of under-vaccinated communities to resurgent preventable diseases.