In late summer and early fall 2020, public health officials in Colorado and nationwide warned about the potential for a looming twin-pandemic. With the weather growing colder, flu season was rapidly approaching, just as COVID-19 cases were beginning to rise to unprecedented levels.
Flu season comes every year, and it often results in thousands of hospitalizations. In the 2019-20 season, for example, more than 3,500 Coloradans were admitted to hospitals with the flu. The prospect of even a thousand flu hospitalizations, in the midst of a pandemic that drove hundreds into the hospital at once, posed a serious threat to hospital capacity.
"I can only imagine how stressful it could've been," Eric France, Colorado's chief medical officer, said in an interview Friday. "In December, our peak hospitalization rate was 1,800 people for COVID. Throw on another 1,000 at that same time for influenza, and it would really have stretched our hospitals."
A few months removed from the end of flu season, which begins in the fall, peaks in the winter and ends in the spring, France said he'd never seen such low numbers of flu cases "in my lifetime." While there were thousands of flu hospitalizations in the 2019-20 season, there were just 34 in the entirety of the most recent season. There've been more than 32,000 Coloradans hospitalized with COVID-19 by comparison. At one point in November, hospitals here admitted more than 2,000 COVID-19 patients in one day.
The cratering of flu hospitalizations is likely due to a number of factors, public health officials said this week. Flu, like COVID-19, is a respiratory illness; the mitigation measures used to blunt the new virus — masking, social distancing, good hand hygiene — all had the dual effect of slowing the flu. Schools, a typical driver of flu spread, were closed for months. That further limited how flu could travel from students to families to the broader community.
It's unclear, experts said, which of those factors played the biggest role in keeping flu at bay this year. But there's little doubt that the response to COVID-19 was more successful at stopping the flu than the new virus.
"We know that for influenza — at least we think — that school-aged children and children in school are a significant way that influenza gets spread around, so that probably had something to do with it," said Lisa Miller, an epidemiologist with the Colorado School of Public Health. "I don't know if anyone knows how much each of those factors made a difference. But I think it makes sense."
Regardless of the exact reasons, France was effusive in describing the "great story" of influenza this year.
"As a country, as it was attending to the COVID pandemic, we didn't recognize something marvelous and astounding that was happening, which was the complete absence of influenza in our community," France said. "… A 99% reduction in hospitalizations compared to the prior year."
According to state flu data, there were 61 flu outbreaks in long-term care facilities in 2019-20. In late 2020 and early 2021, there were zero. Three children died of flu last year. Zero died this year. There were fewer than three flu deaths total statewide; state data does not provide a specific number if the total is below three, in order to protect patient privacy.
Pneumonia, which is often associated with the flu because the latter can lead to the former, also saw a dramatic decrease in deaths. in 2019-20, the respiratory disease killed 268 Coloradans. That death toll has routinely topped 300 in recent years. Since 1999, it's surpassed 400 deaths 14 times.
In the 2020-21 flu season, pneumonia killed 180 Coloradans.
Along with COVID-19 measures, experts attributed the success in part to improved vaccinations. In 2019-20, just over 2 million Coloradans received the flu vaccine. That jumped to 2.27 million last year, according to data provided by the state Department of Public Health and Environment.
Judy Shlay of Denver Public Health said Denver doubled the number of flu vaccines it distributed this past year. In 2019 and early 2020, the health department doled out a little over 110,000 doses, she said. Over the past year, that grew to more than 220,000.
But Shlay and Miller were concerned about the upcoming flu season. The mask mandates, coupled with business and school closures, have ended. It will be virtually impossible to duplicate the efforts that made this year so mild.
"People aren’t physically distancing, people are going to concerts, they're going to ball games, they're going to restaurants," Shlay said. "Masks are really effective. Masks are like getting a vaccine in a sense. They really reduce transmission of infectious disease, and people aren’t masking like they were. I think that, while we hope that hand hygiene is still high, people have probably relaxed that, too."
It's impossible to predict what this season will bring, Miller said. Typically, public health experts monitor flu spread in the Southern Hemisphere, where the flu season occurs in our summer months. So far, there's been minimal influenza in that part of the world. But COVID-19, and countries' varying approaches and present situations, makes it harder to draw comparisons now.
"I would think we’re going to see more flu, but how much more is a big question," Miller said. "And there’s a big difference between what we typically see and what we saw last year. Somewhere in between there is a lot of room. Last year, we saw 34 hospitalizations; the two previous years, it was between 3,500 and 3,800. … We just saw a tiny fraction of that last year. So, where in between those numbers we’ll be, I think it’s very unclear."
France noted that the past year has normalized masking among the general public, and there's bountiful evidence — just look at the flu numbers — that the face-coverings are effective. But after a year of requiring mask use, it's unclear if the general public has any appetite for donning them again to slow a virus that's much more present in every day life.
"Just kind of looking around and observing what people are doing right now, it’s hard to imagine that they're going to change their behavior a whole lot," Miller said. "It might be something that we could influence more from the public health side, but I think people were ready to get back to being maskless, and not social distancing, and I'm not sure how willing they would be to do that to prevent influenza."
There likely will be some who keep wearing face coverings into the future. France, Miller and Shlay all said they plan to continue the practice. They all urged Coloradans to re-up their flu vaccines heading into the upcoming season.
Still, despite the looming unknowns, France celebrated the past season's success.
"I don't know if you’ll ever see that again in your life," he said.