Over 100 children at the school are susceptible to virus.

Florida health officials on Sunday announced an investigation into a cluster of measles cases at an elementary school in the Fort Lauderdale area with a low vaccination rate, a scenario health experts fear will become more and more common amid slipping vaccination rates nationwide.

On Friday, Broward County Public School reported a confirmed case of measles in a student at Manatee Bay Elementary School in the city of Weston. A local CBS affiliate reported that the case was in a third-grade student who had not recently traveled. On Saturday, the school system announced that three additional cases at the same school had been reported, bringing the current reported total to four cases.

On Sunday, the Florida Department of Health in Broward County (DOH-Broward) released a health advisory about the cases and announced it was opening an investigation to track contacts at risk of infection.