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Colorado is having another good flu season so far. But that could change.

Flu vaccinations are running behind last year’s record pace, causing some worry among health officials

Three-year-old Dylan Scully of Lakewood receives a kids’ influenza vaccination from Kaiser Permanente registered nurse Amy Roscoe, right, while visiting a Kaiser Permanente outdoor flu vaccination center in Ken Caryl with his brother Kellen, 6, and their mother, Jennifer Scully, left, on Friday, September 18, 2020. (Andy Colwell, Special to The Colorado Sun)
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Last year, Colorado’s flu season was virtually nonexistent.

Only 34 people were hospitalized for the flu during the entire 8-month season in 2020 and 2021. There were zero reported flu deaths among kids.

This year, the flu season is, well, existent. There have been at least 36 flu hospitalizations so far, a number that started the month at around half that sum then doubled in a single week.

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“It’s not a huge number but the fact that it doubled over the last week is concerning,” said Heather Roth, the Colorado Department of Public Health and Environment’s Immunization Branch chief.

Flu vaccination rates are down compared to last year, as well. So Roth is remaining vigilant. It would not be unprecedented for a flu season that starts out calm to roar to life after the New Year.

But there are also reasons for optimism. No kids have died from the flu so far this season. During the most recent pre-pandemic flu season, the 2019-20 season, nearly 200 people had already been hospitalized with the flu by this time — five times as many people as we’ve seen this year.

Though vaccination rates are behind last year’s record highs, they are in line with previous years’ numbers. And Roth said vaccinations also appear to be picking up.

As of last week, the state had administered about 1.6 million doses of flu vaccine. In the previous year, it had already administered 1.8 million doses by this time. But the number of flu vaccinations administered weekly has begun to outpace last year’s weekly trends.

“It could be people are just waiting a little bit longer and all-told we’ll measure up pretty well to last year,” Roth said.

Here’s more to know about the flu season this year:

It’s definitely worse than last year

This graph, produced by the Colorado Department of Public Health and Environment, shows trends in flu-like illness seen at Kaiser Permanente facilities (top) and emergency rooms (bottom) across Colorado. The red line shows trends for the 2021-2022 flu season, while the purple line shows trends for 2020-2021 and the turquoise line shows baseline levels. (Provided by CDPHE)

Last flu season, amid waves of stay-at-home orders and other social-distancing measures meant to slow the spread of the coronavirus, the U.S. saw one of the weakest flu seasons on record. Months went by with relatively few people showing up in hospitals or doctors’ offices with cases of the flu.

This year is worse — but still not exactly bad. About 3% of people currently seeking treatment at Kaiser Permanente offices have influenza-like illness, well below the baseline of 5%.

It’s worth noting that the flu season officially begins in October each year. In the graphs above, the small spikes occurring at the end of last flu season were happening in September of this year, a prelude to the higher flu activity of this season compared with last.

There’s precedent for a flu season starting mellow and turning bad

This graph, produced by the Colorado Department of Public Health and Environment, shows flu-associated hospitalization trends in Colorado for the current season (shown in red) and previous six seasons. (Provided by CDPHE)

The flu season typically peaks in January or February. But, in some years, it doesn’t peak until March.

That’s why the calm start to this season could be a good sign — or it could be deceptive. 

The graph above shows this year’s remarkably low rate of cases (in red) compared to prior years. But focus for a minute on the light green line representing the 2015-16 season. It, too, started out slow. Then took off around the end of February.

To Roth, this shows that, despite the good start this year, it’s not time for Colorado to get cocky. Getting vaccinated against the flu is still important, as is practicing good hand-washing and staying home when sick.

“I think there’s definitely the potential for things to get bad,” she said.

Among kids, the biggest worry right now is RSV

This graph, produced by the Colorado Department of Public Health and Environment, shows trends in pediatric hospitalizations related to flu (shown in blue), COVID-19 (in red) and RSV (in green). The rates for flu and COVID are for the entire state, while the rates for RSV are only for Adams, Arapahoe, Denver, Douglas and Jefferson counties. (Provided by CDPHE)

Kids and older adults typically bear the brunt of the flu season. That’s true this year, too. Among the small number of hospitalizations so far, those 65 and older and those 5 and younger have the highest rates.

But flu isn’t the most significant respiratory virus stalking children right now in Colorado — nor is it the second-most significant. Estimates of hospitalization rates for RSV — respiratory syncytial virus — were 82 times higher than those for flu in November. Pediatric hospitalization rates for COVID-19 were also significantly higher.

COVID hospitalizations far exceed even the worst flu seasons

This graph, produced by the Colorado Department of Public Health and Environment, shows trends in hospitalizations related to flu (shown in the blue lines) and COVID-19 (shown in red). (Provided by CDPHE)

There really is no comparison between the flu and COVID. Hospitalization rates for the coronavirus have far exceeded flu hospitalization rates for all recent years. In November, the hospitalization rate among all age groups for COVID was 188 times higher than the hospitalization rate for flu.

But, Roth said, this is all the more reason to take the flu seriously. Even though the risk of hospitalization is lower, now is not a good time to take that gamble.

Hospitals remain crowded places. Even though COVID hospitalizations have fallen in recent weeks, more than 1,300 people are currently hospitalized with the coronavirus in Colorado. The state’s hospital intensive-care units are 95% full and, according to federal data, nearly 38% of people in the ICU in Colorado are there with COVID.

Getting vaccinated against both the flu and COVID will help reduce the strain on hospitals and also reduce the likelihood that you will end up in the hospital with either, Roth said. A flu vaccine can also limit the risk of passing the virus to someone who is vulnerable. The COVID and flu vaccines can be administered at the same time — just in different arms or, at least, 1 inch apart from one another in the same arm.

About 56% of Coloradans 65 and older have gotten a flu vaccine this year, Roth said. But only about 18% of those ages 20 to 39 have.

“I think sometimes people think they may have missed the window on flu vaccination because we start hammering them pretty hard in October,” Roth said. “There’s this belief that you need it before Halloween, and that’s not true. You really should be getting your vaccine as long as the virus is circulating.”