Strange spike in spring flu likely related to COVID-19

A strange spring spike in flu cases has hit Colorado this year as many people also struggle with COVID-19 infections and spring allergies. Photo: Getty Images.

Colorado has seen a strange spike in spring flu cases this year, and like many other trends in the post-pandemic world, this year’s unusual flu season is likely related to COVID-19.

“It’s wild. It messes everyone up,” said infectious disease expert Dr. Michelle Barron, on the 2022 flu season. “In the past few weeks, a lot of people have gotten sick with the flu. It is here. Many of us got the flu shot in August. The vaccine may not have been perfect for this year’s flu. And any protection we had is probably worn out by now.”

Flu cases spiked in April and May at the same time Colorado was experiencing a new wave of COVID-19 cases. One could describe the convergence of influenza and COVID-19 infections as a kind of “twindemic”.

“It’s the weirdest flu season I’ve ever seen,” said Barron, senior medical director for infection prevention and control at UCHealth University of Colorado Hospital on the Anschutz Medical Campus.

Along with the spread of flu and COVID-19, many people suffer from seasonal allergies when spring plants are in bloom. Those with a head cold or pain can’t be sure what’s making them sick unless they’re tested for COVID-19 and the flu.

Typically, flu cases in North America peak during the winter months of December through February. This year, flu cases in Colorado’s most populous counties began to rise in December and then fell to unusually low levels in January and February. They then slowly began to rise again in March, reaching very high levels in April and May.

Barron sees a direct connection between the end of the COVID-19 mask requirement and the spring surge in flu infections.

“It’s all related to COVID-19,” Barron said

“In February and March, when people stopped wearing masks, we started seeing a spike in flu cases. Through April and May, there were more than 1,100 cases per week (in Colorado’s most populous counties),” Barron said.

In addition to people not wearing masks in the spring, protection from flu shots also decreased in the fall.

Take a look at the chart below and you’ll see a visual representation of weird flu trends. Tri-County Health monitors flu cases and has created a chart that shows some strange patterns. Colorado flu cases for 2022 appear in green. The spring peak this year reached a level almost as high as infections during the 2019-2020 flu season (marked with a red line), just before the start of the COVID-19 pandemic. The following year, winter 2020 and 2021, there were almost no cases of influenza due to all the efforts to contain the COVID-19 infections (denoted by a flat line below).

Chart showing springtime peaks for influenza cases in Colorado.  Chart courtesy of Tri County Health.
The green bars show flu cases in Colorado’s most populous counties during the 2021-2022 flu season. Colorado is experiencing a strange spring spike in flu cases. The other peak shows influenza cases in 2019 and 2020, which reached high levels during the winter months (typical for influenza) before COVID-19 infections triggered a global pandemic. Chart courtesy of Tri-County Health.

The 2021-2022 flu season appeared to start normally in December. Then the Delta COVID-19 variant arrived, followed by omicron and its variants.

Barron believes people wore masks during the winter months and were cautious in crowded indoor spaces.

“That probably quelled the flu for the first few months,” Barron said.

Then politicians started lifting mask mandates. Tired of worrying about COVID-19, many people took off their masks. And guess what? The influenza virus, which like all other viruses is opportunistic and finds hosts where it can, spread more easily in the spring.

What will happen this summer and fall related to flu and COVID-19? That remains unclear. Barron keeps a Magic 8 Ball on her desk at work and often jokes about her inability to predict the future. All humor aside, Barron is concerned that the flu could remain pervasive as COVID-19 infections continue to spread.

In typical years, influenza “A” spreads first, then influenza “B” takes over and later causes infections. This year, the flu cases that caused the springtime spike have all been linked to the “A” strain.

It’s possible that influenza “B” could circulate in the summer while COVID-19 variants continue to spread.

How to find out if you have spring flu or COVID-19

So what should you do when you feel sick?

Get tested, advises Barron.

Since COVID-19 is widespread, you can first get tested for the coronavirus.

“If you test negative for COVID-19 and have not been in contact with people with the flu, you could get a false negative for COVID-19 or have the flu. The symptoms are similar: fever, body aches, cough,” Barron said.

In addition, a small number of people have contracted COVID-19 and the flu at the same time.

That kind of double whammy isn’t common, Barron said.

Still, it’s good to get tested. COVID-19 testing is available both at home and in healthcare facilities. Please note that home tests are not as reliable as a nasal swab or PCR test. You can get false-negative results with a home test. So if you’re feeling sick, be careful about embarrassing other people.

Visit your doctor’s office for a flu test.

If you test positive for either the flu or COVID-19, there are treatments you can receive to shorten the duration of your illness or reduce its severity. Barron advises people to act quickly.

The antiviral drug that helps fight the flu is called Tamiflu and people need to start taking it quickly, within about 48 hours of the onset of symptoms.

If you test positive for COVID-19, you may also be able to receive additional treatments. It’s best to start these treatments within about five days of the onset of symptoms.

As people deal with a crazy constellation of diseases this spring, researchers are working on vaccines for the fall. Stay up to date on vaccination news all summer long. It is possible that a combined vaccine against influenza and the latest strains of COVID-19 will be available in the fall. If not, we could be in for another heavy wave of multiple viruses.

“I’m really worried about the fall. COVID-19 is likely to increase again. Our immunity is suppressed and new variants may emerge,” Barron said.

Fortunately, both vaccines and new treatments are making flu and COVID-19 a little less dangerous.

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