RICHMOND, Va. (AP) — Officials say almost half of all sixth-graders in Richmond public schools missed class this year because they were not properly vaccinated.

Last year, 760 students had not received their Tdap vaccine, which guards against tetanus, diphtheria and pertussis, on the first day of school.

The Richmond Times-Dispatch reports that’s up from 2015, when 516 sixth-graders, or 33 percent, had not received their Tdap vaccines.

In an effort to boost vaccination compliance, public health officials are working to bring nurses to schools to vaccinate fifth-graders before the summer.

Officials say vaccination rates have plateaued statewide recently, which state health officials attribute to a rising anti-vaccine movement.

But records show that only seven Richmond sixth-graders submitted religious or medical exemptions last year, suggesting there other reasons for children not getting vaccinated.