Utah health officials predicted many more cases of COVID-19 in schools than we’ve seen. Why was their model so off?

The state health department refused to answer questions about its analysis.

(Trent Nelson | The Salt Lake Tribune) Students wearing masks work in Elizabeth Kunz's second grade class at Neil Armstrong Academy in West Valley City on Tuesday, Sept. 28, 2021. The Utah Department of Health says there were fewer cases of COVID-19 in classrooms last month than anticipated.

There were far fewer cases of COVID-19 in Utah schools last month than state health officials had predicted — and they’re not sure why.

The Utah Department of Health had gone into this school year with a dire model, anticipating that the virus would spread quickly among K-12 students with a new, more contagious strain and no statewide mask mandate. It estimated that there would be 39,000 cases in just the first 30 days.

But a month in, there were only about a quarter of that many infections. The numbers for the end of September showed 9,957 reported cases among school-age children.

“We were way off,” the department said in a series of tweets from last weekend.

The actual total was still more than the number of cases recorded for same time period in fall 2020, when there were slightly more than 3,000 cases among school-age children 30 days into classes. The department’s model, though, expected it to be 13.9 times higher, not the 3.6 times that it ended up being.

So what happened? State health officials apparently don’t know.

A spokesperson for the department said officials would not be commenting beyond the tweets. When pressed, the spokesperson noted they are “not sure we really know” what made the difference in the prediction versus the reality.

Nicholas Rupp, the spokesman for the Salt Lake County Health Department, said: “It is worth noting that our understanding was the model was designed to predict the worst-case scenario for planning and preparation purposes — and we are grateful we didn’t see that come to fruition.”

The state’s model, according to the state health department’s tweets, was based on the vaccination rates of teenagers in Utah, immunity from past cases among school-age children and the rate of transmission of the virus.

None of those have changed significantly in the past month. In fact, as the state’s coronavirus response team tweeted Tuesday, many kids 12 to 17 years old who are eligible for the vaccine still haven’t gotten their shot.

“There is only one health district with more than 60% of children who are fully vaccinated against COVID-19,” the tweet notes. That’s Summit County in northern Utah, which is close to 80%.

The tweet continues: “One health district has less than 20% of children fully vaccinated.” That’s the TriCounty Health Department’s jurisdiction in east-central Utah that includes Daggett, Duchesne, and Uintah counties. It also has the lowest overall vaccination rate among eligible adults, at 28%.

Salt Lake County, which has the highest concentration of students in the state, is hovering in the middle around 60%. Those numbers are pretty close to what they were a month ago.

At the same time, the immunity from past cases wouldn’t have changed recently; that occurs after a kid, for instance, has been sick and then has natural antibodies that fight against the disease.

That leaves the only other factor that the state listed as part of its model: transmission rate. That is also unlikely to have decreased significantly because cases have continued to spike across the state in other ages groups.

There’s a possibility, though, that some efforts have slowed spread beyond expectations, such as masking in schools.

When the state department created its model, it was before the school year started and no district or charter had a mask mandate. The state Legislature has banned schools from creating those requirements this year.

Instead, for a school to mandate face coverings, an order has to come from a county health department and be approved by a county governing body. Currently, both Grand County School District and Salt Lake City School District have one in effect.

Those cover roughly 22,000 kids between the districts; there are 665,000 total in the state. Is that enough to make a difference in transmission rates?

At 3% of the public K-12 school population here, probably not. But if enough parents and kids are voluntarily electing to wear masks in other districts, too, there’s potential.

And Dr. Angela Dunn, former state epidemiologist and now the executive director of the Salt Lake County Health Department, noted in a tweet Tuesday that Salt Lake City School District does have the lowest transmission rate of any of the five public districts in the county. (She had tried to issue a mask mandate for the full county, but it was voted down by the Salt Lake County Council on party lines.)

The other possibility is that parents are refusing to get their child tested for COVID-19 even if they show symptoms or have been exposed. The state health department has already said that some parents have been declining to talk when their kid does test positive. So it’s likely some in more conservative areas are forgoing tests altogether.

With some of the Test to Stay events, too, that the state has conducted after outbreaks at schools, parents have opted not to have their kid participate. At American Preparatory Academy’s Draper 2 campus, for instance, about 400 of the 1,200 kids there did not have permission to be tested. Under the protocol, students who test negative can continue to attend classes in person.

It’s unclear, though, how large that number may be statewide. And just refusing to test doesn’t mean all of those students would be positive. So it’s not likely to make a difference of 30,000 students that the state overestimated in its model.

But the state has declined to answer to whether either masks or not testing were contributing factors to the problem, or if it was a combination of both.

“Public health modeling is complex,” the Utah Department of Health noted in its tweets Saturday. “It tries to predict behavior from a few simple measures seen in the past.”

The department stated only that it’s happy that the model was off “in the ‘right’ direction.”

“The data from the first weeks of school this year are promising,” the department said. “We will continue to be transparent and provide accurate information to all Utahns about #COVID19. We will continue to learn and grow as we respond to this disease.”

The thread was filled with comments from people accusing the department of purposefully trying to scare parents. One wrote: “Thank you for admitting your fear-mongering.”

Others, though, thanked the department for the honesty and said it’s still upsetting that more than 9,000 kids have gotten sick from COVID-19 this school year.