Idaho’s child immunization rates improved in 2015, reaching a five-year high.

And Department of Health and Welfare officials don’t know what to make of the numbers yet.

In 2015, 86.7 percent of Idaho students were considered “adequately immunized,” according to Health and Welfare spreadsheets obtained this week by Idaho Education News. The 2014 figure was 85.6 percent.

Boosting childhood immunization rates is a priority for public health officials, and not just in Idaho. Health officials say a robust vaccination rate doesn’t only protect children who are current on their shots. A higher vaccination rate protects children who aren’t current on their shots because it decreases the risk of an outbreak of disease — a concept known as “herd immunity.”

The new immunization rate still falls short of Idaho’s 90 percent goal. However, it represents the third successive increase in statewide rates.

About the numbers

Health and Welfare collects immunization data for kindergartners and first- and seventh-graders. Numbers from those three grades are tallied, and that’s how Health and Welfare calculates the 86.7 percent figure.

Idaho Education News analyzed the results by school district (click here to see how your district stacks up.) Here are some key findings:

• Thirty-eight of Idaho’s 115 school districts met the state’s 90 percent target. The list includes some small districts with small student populations. Significantly, several of the state’s largest districts hit the 90 percent mark: West Ada, Boise, Nampa, Idaho Falls, Pocatello, Bonneville and Vallivue.
• For kindergartners, 31 districts reached the 90 percent mark.
• Three small and rural districts — Cambridge, Salmon River and Swan Valley elementary — reported immunization rates at or below 50 percent. The tiny Avery school district in North Idaho reported no data for its one kindergartner and one first-grader.
• Immunization rates lagged below the state average at charter schools (80.9 percent) and private schools (77.3 percent).

What happened?

That’s still a mystery to Health and Welfare officials, who only received the new numbers last week.

It will take the agency a few weeks to crunch the raw numbers and look for trends, spokesman Tom Shanahan said Wednesday.

But Shanahan pointed out one takeaway: It appears that fewer parents filed for — and received — a written exemption from vaccinations.

Parents can request an exemption, citing medical, religious or philosophical reasons. Exemptions are easily obtained, and exemption forms are readily available on Health and Welfare’s website. Agency officials believe some parents file for an exemption because it’s easier than taking their children in for vaccinations.

In 2014-15, 6.5 percent of kindergartners were exempted from at least one vaccination. This rate ranked highest in the nation, and Health and Welfare labeled the number “concerning.” For 2015-16, the exemption rate dropped to 6.3 percent for all students, and 6.1 percent for kindergartners.

How does Idaho stack up?

It’s too early to tell how the new numbers will affect Idaho’s national rankings.

But in August, the Centers for Disease Control compared 2014-15 kindergarten immunization rates, and Idaho fared poorly.

For example, 89.5 percent of Idaho kindergartners were current on their measles, mumps and rubella vaccinations, ranking No. 45 nationally. Idaho’s vaccination rate for diphtheria, tetanus and acellular pertussis ranked No. 48 in the nation.