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When Dr. Jessica Cataldi, a professor of pediatrics at the University of Colorado School of Medicine and a practicing pediatrician at Children’s Hospital Colorado, was doing infectious disease work in Africa years ago, she noticed a difference in how many parents there thought about vaccines.

Resistance to vaccination exists across the world for a variety of reasons — from spiritual belief to experiences with prior botched vaccination campaigns. But Cataldi said parents were generally more willing to vaccinate their kids when the diseases were active threats in their communities, meaning their children might get sick without a vaccination.


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Back home in the United States, vaccines have largely eradicated infectious diseases of the past — like measles and polio — and that, too, has shaped how parents view vaccines, Cataldi said.

“It’s a difference thinking about the risks and benefits,” she said. “People who see kids getting sick more often, they understand the risk from those diseases. When the diseases are less common, there is a shift to thinking more about the risk of the vaccine.”

That insight helps explain Colorado’s arduous struggle to get childhood vaccination rates above 90% statewide, a goal achieved this year just before the coronavirus pandemic hit and likely knocked them back down again. But it also provides a hint at one of the biggest unknowns surrounding vaccines for COVID-19 that are fast heading toward market: Once they’re approved, how many people will actually want to use them?

Because it is possible that the coronavirus vaccines won’t be 100% effective for everyone, their value may lie more in their ability to bring an entire population to the level of herd immunity — where not everybody is immune but just enough are to prevent the virus from spreading. But reaching herd immunity through a partially effective vaccine requires lots of people to get vaccinated. And Colorado’s struggle with childhood vaccination rates shows why that could be difficult.

CDPHE Executive Director Dr. Jill Hunsaker Ryan speaks to reporters at a coronavirus testing site set up at Water World in Federal Heights on Monday, Aug. 10, 2020. (Jesse Paul, The Colorado Sun)

The long climb to being not last

For years, Colorado has ranked among the lowest in the nation for the vaccination rates of kindergarteners.

Last school year, the rate of measles vaccination for Colorado kindergartners was around 87%, two full percentage points below the second-lowest state, Idaho, according to the federal Centers for Disease Control and Prevention. Colorado was the lowest in the country for the chickenpox vaccine, the polio vaccine and the hepatitis B vaccine and second-lowest for the DTaP vaccine, which protects against diphtheria, tetanus and whooping cough.

But after increasingly strict enforcement of vaccination rules in schools and more-focused work by public health officials targeting problem areas, those rates started to climb. When leaders at the Colorado Department of Public Health and Environment convened a virtual news conference last month to announce the rates for the 2019-20 school year, they sounded practically giddy.

The measles vaccination rate had climbed to 91%, CDPHE executive director Jill Hunsaker Ryan said, and rates for all other recommended vaccines were above 90%.

“It’s really a collaboration success story,” she said.


The CDC has not yet released nationwide rankings for this year’s kindergarten vaccination rates. A 91% rate would have placed Colorado fifth-to-last in the 2018-19 rankings. And all of Colorado’s kindergarten rates still fall below the 95% level that the CDC recommends as a target.

There was another caveat during that announcement. The state’s survey of vaccination rates had taken place prior to the pandemic’s onset. And, during the first months of the pandemic, state reports suggest that about 19% fewer kids have gotten vaccinated than did during the same months of 2019.

“These declines in vaccination rates that we’ve observed do put us at risk for another serious public health crisis, in addition to the COVID crisis,” state epidemiologist Dr. Rachel Herlihy told reporters.

Parents and children gathered in front of Colorado’s state capitol on March 9, 2020 to pay tribute to children who died after having received a vaccine. The vigil was organized by the Colorado Health Choice Alliance –– an anti vaccination advocacy group. The gathering was also in opposition of Senate Bill 163, which would require parents who choose not to vaccinate their children to get a medical provider to sign off on it. (Moe Clark, The Colorado Sun.)

Access and acceptance

There are two main reasons kids go unvaccinated, reasons that could also provide useful guidance for health officials hoping for a broad embrace of a coronavirus vaccine. One is access — do people have affordable places they can go to get vaccinated? The other is acceptance — do people want a vaccine for themselves or their children?

Both issues are present in Colorado, Cataldi said.

About a quarter of Colorado child care centers, kindergartens and K-12 schools have average immunization rates across all vaccines below 90%, according to a Colorado Sun analysis of state vaccination data. But likely fewer than 1% of centers, kindergartens and schools have average vaccination rates below 50%. (There are a small number of schools listed in the data as having vaccination rates of 0%, which could be in error, hence the slight uncertainty.)

There’s no strong correlation among those at the very bottom. They occur along the Front Range and in rural Colorado; they are public and private. The K-12 school with the lowest average vaccination rate in the state, according to CDPHE data, is a private school in Colorado Springs affiliated with a Baptist church. A third of the students there have either a religious or personal-belief exemption from vaccination requirements, but the low rate is also driven by the school’s high rate of students for whom it has no vaccination or exemption records.

The public K-12 school with the lowest average rate is the North Fork School of Integrated Studies, a magnet school in Paonia that describes itself as “Waldorf-inspired.” Roughly two-thirds of the kids at the school have a personal-belief exemption. (The liberal Waldorf educational movement emphasizes arts, the outdoors and experiential education, with no textbooks until sixth grade. Waldorf schools nationally have been linked to outbreaks of vaccine-preventable illness and generally have extremely low vaccination rates, which is true in Colorado, as well. The Delta County School District, which includes the NFSIS, did not respond to a request for comment for this story.)

But Cataldi said perhaps the bigger challenge is getting to areas where parents and kids want to be vaccinated but don’t have adequate access to medical care.

“We do know that access is an issue, particularly in some rural areas,” she said.

A researcher at Fort Collins-based BioMARC holds up samples of culture material that represent the starting place for growing out large viral stocks on October 9, 2014. BioMARC, which manufactures vaccines, is working with scientists from CSU’s Infectious Disease Research Center on a vaccine for COVID-19. (Provided by Colorado State University)

Lessons for a COVID-19 vaccine

Vaccination experts said the state’s experience with childhood vaccines provides guidance for how to encourage people to get a future COVID-19 vaccine — but only to an extent.

Cataldi said it will be important for researchers to show that the vaccines are safe to counter fears over the vaccine’s newness. When the HPV vaccine became available, for instance, Cataldi said parents had lots of questions about how it was developed and tested and whether it was worth it.

“It’s important that we develop a safe vaccine because we don’t want people to get sick,” she said.

May Chu, a clinical professor in epidemiology at the Colorado School of Public Health, said it will also be important for researchers to be transparent in showing the vaccine is effective, in order to overcome the distrust of authority that often drives vaccine hesitancy.

“All that data should be published,” she said. “It should not be a statement by someone standing at a lectern saying it works.”

The state will also need a plan for making sure the vaccine gets to hard-to-reach communities and can be available to people regardless of their ability to pay.

But Cataldi said children’s vaccinations programs are not a perfect model for how to boost COVID-19 vaccination. That’s because adults will probably be the first target for a coronavirus vaccine — and the data on adult vaccinations is a lot murkier because there aren’t the same reporting systems as there are with kids.

“We know almost nothing about whether adults living in Colorado got the vaccines as a child,” she said.

We do know how many adults get the flu vaccine every year, and it’s not exactly encouraging for those hoping for widespread adoption of a coronavirus vaccine. During the 2018-2019 flu season, the most recent one for which numbers are available, about 48% of Coloradans got a flu shot — putting the state about three percentage points above the national average, according to the CDC.

CDPHE’s Ryan said the state is hoping to get that number up for the coming flu season, in the hopes of avoiding a flood of flu patients colliding in hospital intensive care units this winter with a flood of coronavirus patients.

“We don’t want to go backwards in our immunizations,” she said. “We were doing so well before COVID-19 hit, and I think COVID-19 has shown just how important it is for people to be immunized so we can keep communicable diseases from spreading.”

Chu said the wild card in determining how many people get vaccinated against COVID-19 may be the virus itself. For most people, the vaccines they normally get can seem blandly precautionary — guarding against rare viruses or those that might not seem that bad. And that thinking may hold for coronavirus, too, if other measures are successful at weakening the virus’ spread before a vaccine arrives.

But if the pandemic is raging and one dose might let you go back to your regular life?

“If it’s really in a hot transmission zone,” Chu said, “it’s going to be different.”

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