Dr. Joseph Gigante, a professor of pediatrics at Monroe Carell Jr. Children's Hospital at Vanderbilt, said the hospital treated a child with measles last week. At least nine measles cases have been reported statewide this year, and five of those involved people who were unvaccinated, according to the Tennessee Department of Health.

"I think, unfortunately, this is predictable," Gigante said. "As more and more parents opt to not vaccinate their kids against measles with the MMR vaccine, we're going to see more and more of these outbreaks."

The warning comes as the Tennessee Department of Health's latest kindergarten immunization report shows that only 92.5% of kindergarteners statewide were fully immunized with all six required vaccines at the start of the 2025-26 school year. That is essentially flat from 92.3% the year before and below the 95% threshold public health officials consider necessary to prevent outbreaks.

The share of counties reaching at least 95% immunization has fallen sharply over the past five years, from 76% in 2019 to just 17% in the 2025-26 school year. That is slightly above the 15% recorded for 2024-25.

In Davidson County public and charter schools, 92.9% of students were fully immunized at the start of the 2025-26 year, up slightly from 92.2% the prior year. But 3.7% of students had a religious exemption, up from 3.3%.

Williamson County saw a steeper decline. Just 87.7% of students were fully immunized, down from 90.5% the year before, while 11.1% presented religious exemptions, up from 8.4%.

Statewide, 7.5% of students had a documented exemption, whether religious or medical, the highest share on record and up from 6.6% the previous year. The increase was driven largely by religious exemptions, which rose from 3.5% to 4.6%.

To obtain a religious exemption, parents or guardians must submit a signed statement saying vaccination conflicts with their religious beliefs. A medical exemption requires a note from a physician or public health nurse documenting the risk of harm from specific vaccines, and the child must still receive any vaccines for which they are not at risk.

Gigante said some medical professionals will sign exemptions for students who are not actually at risk of harm, but he said none at Vanderbilt would do so.

He said measles is not the only concern. He is beginning to see children in his clinic with meningitis, haemophilus influenzae and pneumococcus, all of which are preventable by vaccine.

Kindergarten immunization requirements have not changed in recent years, but federal guidance has. Earlier this year, the Centers for Disease Control and Prevention cut its childhood vaccination recommendations from 18 to 11. Gigante and his colleagues have continued to follow the American Academy of Pediatrics' recommendations, which still list 18 childhood vaccinations.

The only addition to the schedule is an optional RSV shot introduced in 2023, which Gigante said significantly reduced hospital admissions for babies and toddlers.

Gigante said vaccine hesitancy is the worst he has seen in more than three decades of practice.

"I've been doing this for over 30 years," he said. "This is the worst it's ever been by far, and I'm afraid it's only going to get worse."

He added: "I don't know how many more measles outbreaks it will take, and to be quite honest, how many more children have to die from measles and other vaccine-preventable diseases before folks decide, 'Hey, maybe not vaccinating our children is not the right choice.'"