Why this state is lagging behind the rest of the US in routine childhood vaccinations

When a recent federal report published last week showed routine childhood vaccination rates had fallen among kindergartners for the 2022-23 school year, public health experts were disheartened to see the drop.

However, there was one state that lagged behind the rest: Idaho.

For all four major vaccines -- measles, mumps and rubella (MMR); diphtheria, tetanus and acellular pertussis (DTaP); poliovirus (polio) and varicella (chickenpox) -- Idaho had the lowest percentage of kindergartners who met school requirements for vaccinations, all around 81% compared to a nationwide rate of 93%.

What's more, Idaho was the state with the highest percentage of exemptions from one or more required vaccines at 12.1%. Comparatively, the rate of exemptions across the U.S. was about 3%.

"This is concerning not only at a state level but nationally, as well, because we're not the only state experiencing this; we just appear to be experiencing it a little more than other states," Dr. Bethaney Fehrenkamp, a clinical assistant immunologist at Idaho WWAMI -- a partnership between the University of Washington School of Medicine and Washington, Wyoming, Alaska, Montana and Idaho -- told ABC News.

Public health experts noted that clusters of unvaccinated or under-vaccinated children can lead to outbreaks of preventable diseases such as measles, which is exceptionally contagious and can lead to serious complications such as pneumonia, encephalitis -- which is inflammation of the brain -- and even death, according to the Centers for Disease Control and Prevention.

In one case, between November 2022 and February 2023, a measles outbreak swept across several schools and day cares in central Ohio, infecting 85 children, 80 of whom were unvaccinated.

In Idaho, there was a measles outbreak last month that infected 10 people, according to the Idaho Department of Health & Welfare. Prior to that, there had been just two cases reported in Idaho in 20 years.

When you have an under-vaccinated population and a contagious disease, "it'll spread and it'll spread more easily," Dr. Kevin Cleveland, an associate professor at the College of Pharmacy at Idaho State University, told ABC News.

The type of exemptions allowed also may pose a problem. All 50 states and Washington, D.C. allow exemptions for medical reasons while 45 states and D.C. grant exemptions on religious grounds, according to the National Conference of State Legislatures (NCSL).

However, there are also 15 states that grant philosophical exemptions due to "personal, moral or other beliefs," the NCSL says. This means that parents can ask for an exemption for their child for just about any reason.

Experts say there are a few reasons why rates might be low. One is access. Idaho is a state with 35 of its 44 counties being rural and 174 physicians per 100,000 people, which may make it hard for people to reach providers or schedule appointments.

Additionally, the rates may be an after-effect of the COVID-19 pandemic. Some of the hesitancy around COVID-19 vaccines may have inadvertently spilled into concerns about other vaccines.

"We've seen a slow but kind of steady increase in vaccine hesitancy but that was exasperated by COVID-19," Fehrenkamp said. "While some of the decreased vaccination rates during the pandemic itself were probably likely due to access and availability and maybe a fear of bringing your child to a health care facility during a pandemic -- potentially, like misinformation and some lack of trust as well as incomplete transparency has also just kind of exasperated that trust, and made it worse."

Cleveland said people may also be experiencing vaccine fatigue after being recommended by health experts to get COVID-19 boosters and updated vaccines to help combat circulating variants at various times.

"Every time we talk about a vaccine, it goes back to COVID vaccine," he said. "I think people are just a little tired. It's like, 'Oh, no, another vaccine.'"

Another reason may be that because these diseases have been circulating at low rates due to vaccines, people have forgotten how serious they were before the advent of vaccines.

For example, in the decade before the MMR vaccine became available, it was estimated that 48,000 people were hospitalized with measles each year and between 400 and 500 people died each year, according to the CDC.

"These diseases are really, really contagious and they're really serious and I think potentially, we've forgotten how serious these diseases can be and we require a certain number of the population to be vaccinated in order to get that protection for those that can't be vaccinated," Fehrenkamp said. "We've previously eradicated these diseases in the U.S., which is why I think maybe, culturally we have forgotten how serious and how detrimental they can be."

To try to increase these numbers, Fehrenkamp said it's important for health care providers to have honest conversations with parents about why they're hesitant or concerned about vaccines to try to assuage their fears.

"I want parents to choose to vaccinate their children, but I want them to feel really good about it and I want them to feel really informed about it and so we need to do a better job informing on vaccine safety," she said.

At Idaho WWAMI, Fehrenkamp said they bring in students from Idaho that have links to underserved communities to help educate them with the hope they'll go back and practice in those areas and fill a health care gap.

Cleveland, who specializes in immunization outreach to underserved populations in Idaho, said it's also important to bring those vaccines into rural or underserved communities to make it easier for people to keep up with vaccine schedules.

"Taking the vaccines to the people, especially in the rural areas or even like workplaces or schools, we usually have really good success in vaccine uptake," he said.