The number of Minnesota schools with low kindergarten vaccination rates for measles and chickenpox has grown sharply in the last five years, prompting concern among state health officials that they are vulnerable to outbreaks of the highly contagious diseases.

One-third of Minnesota schools had kindergarten vaccination rates below the level required for "herd immunity," according to a Star Tribune analysis of 1,110 elementary schools.

Several of those schools have had chickenpox outbreaks since 2017, including one that had two separate outbreaks, according to the Minnesota Department of Health.

Unvaccinated children also helped drive a measles outbreak in 2017 that sickened 75 and sent 21 to the hospital. Nationwide, there has been a resurgence of measles in low-vaccination pockets across the country, with nearly 400 cases last year, according to the U.S. Centers for Disease Control and Prevention.

"We are concerned about these kids," said Dr. Sheldon Berkowitz, president-elect of the American Academy of Pediatrics Minnesota chapter. "It is important to vaccinate not only for your own child but for other children in the community that are not able to get vaccinated."

The falling vaccination rates have triggered concern among physician groups, public health officials and researchers, who are reminding the public that vaccines carry low risks and benefit population health. They cite voluminous medical research, including a recent study which found that there was no link between the measles vaccine and autism, one of the myths that drove down vaccination rates and created fertile ground for the recent Minnesota measles outbreak.

"I think what is driving it is fear and the internet and the idea that there is not science behind the recommendations that we make," said Berkowitz. "They, in fact, are based on very sound scientific information."

Minnesota public health officials say they're concerned about the trend, but note that overall statewide kindergarten vaccination rates are high — 93 percent for measles and 92 percent for chickenpox.

"When you vaccinate your kids, you are the norm," said Kris Ehresmann, infectious disease director at the Health Department. "The people who don't vaccinate … are a small outlier but an outlier that has grown, so we are concerned about that."

Fully 787 of the schools with kindergartens had measles vaccination rates at or above the 90 percent level in the 2017-2018 school year, the most recent available data. Collectively they enroll four-fifths of the state's kindergartners.

But those numbers mask the pockets of lower rates where diseases can spread easily in close quarters.

The trend is driven in part by the rising number of parents who choose not to vaccinate their children, as allowed under state law, but could also include children with incomplete doses or whose parents haven't filed the required paperwork with schools.

Whatever the reason, more schools now fall below the 90 percent threshold for the measles, mumps and rubella (MMR) vaccine rates. Last year it was 30 percent of all kindergartens, an increase from 22 percent five years earlier. During that period, 150 schools saw their vaccination rates drop more than 5 percentage points, dragging them below the 90 percent level.

For chickenpox, 33 percent of schools are below the 90 percent immunity threshold, a number that public health officials say is the lower limit necessary to prevent outbreaks.

Schools report vaccination rates for kindergartners and seventh-graders only. Vaccination rates improve at the higher grade, where only half as many schools fall below the 90 percent threshold for the MMR and chickenpox.

Many of the pockets are in small charter and private schools, where a handful of unvaccinated kids in a small kindergarten population can drive the vaccination rate below the recommended threshold.

Still, fully one-fifth of the state's kindergartners are enrolled in these "pocket" schools, and even though most of those children have the recommended two doses of the MMR vaccine, they are also at risk because the vaccine does not provide complete protection.

'Puts us on high alert'

In addition to the risk of an outbreak, students without shots can endanger other children who cannot be vaccinated for medical reasons. Many of these children have weakened immune systems caused by a chronic illness or medical treatment. Getting a shot such as the MMR, which contains a live but weakened form of the virus, could actually make them sick. And if they caught the disease from someone else, they would most likely develop severe symptoms.

"It is something we think about all the time," said Linsey Rippy, who has two daughters who have had heart transplants. They take medications that prevent their bodies from rejecting their hearts, but those drugs also sap their ability to fight disease.

"The people that are around my kids have to be vaccinated, so we know that we are giving them as much of a safety net as possible," Rippy said.

At the start of every school year, Rippy writes a letter to her children's teachers and asks them to pass it along to all the parents about the importance of vaccinations. "It is not for me to know whether their kids are vaccinated," she said. "But it is my hope at least that they understand a little bit more of what we have gone through and why we feel the way we do."

With recent reports of measles outbreaks nationwide indicating a growing reluctance about vaccines among parents, Rippy worries that schools will lose the herd immunity that helps protect her children.

"It puts us on high alert," she said.

Minnesota is one of 17 states that allow parents to opt out of immunizations for personal reasons. All states provide exemptions for medical reasons, while others stipulate that exemptions must be based on religious beliefs.

Kelly Johnson, whose 12-year-old daughter attends a public school and has never been vaccinated, is one of the vaccine skeptics.

"I just fill out the conscientious objector form," Johnson said. "That is a right that Minnesota parents have."

Johnson started questioning vaccines after her older daughter started having seizures at a young age. She believes the MMR vaccine was responsible, but she also traces other medical problems, including chronic ear infections, back to vaccines her daughter received when she was 2 months old.

The seizures never stopped, and today her 20-year-old daughter is in a wheelchair.

Johnson also has a 21-year-old son who was vaccinated and has had health problems, including asthma and severe allergies.

"I have this small, minute study in my own household and it is fascinating how much healthier my unvaccinated child is," she said. "I feel like it is our right as parents to do what we feel we need to do for the health of our own children."

One school, two outbreaks

The rising number of schools with substandard chickenpox vaccinations has coincided with an uptick in outbreaks of the disease.

Maranatha Christian Academy in Brooklyn Park was one of four schools that had chickenpox outbreaks in 2017. With 84 percent of its kindergartners and seventh-graders immunized, including those who acquired immunity through illness, the school saw seven cases of the disease.

By 2019, immunity at Maranatha had risen to 92 percent for kindergartners and 90 percent for seventh-graders, but the school saw another outbreak, this time nine cases.

"I don't want to see these diseases back in schools," school head Brian Sullivan said in an interview.

Increasingly, Sullivan said, vaccinations have become a polarizing issue among parents. "It is a challenging situation. The law allows parents to opt out," he said. "We can't usurp their authority."

Sullivan said he has heard concerns from some parents about others who choose not to vaccinate.

The school's role is primarily to collect documentation of shots or exemptions from parents and to inform the school community of any health issues, such as outbreaks.

"We are limited by the parameters of the law," he said.

Last year, Eagle Ridge Academy, a charter school in Minnetonka, had documentation of the MMR immunization for just 66 percent of the 136 kindergartners enrolled.

"We have a high Somali population and there is a belief in that community that it has ill effects, especially the MMR," said Executive Director Jason Ulbrich. "It is just false."

To improve its reporting rate, the school held parent meetings before the current school year to explain the importance of vaccines. Since then, rates have improved 10 to 15 percent, he said.

"We are trying to educate them and get the information in their hands," said Ulbrich.

Glenn Howatt • 612-673-7192