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

“It’s wild. It’s throwing everyone for a loop,” infectious disease expert, Dr. Michelle Barron, said of the 2022 flu season. “A lot of people have caught the flu in the last few weeks. It’s here. A lot of us got our flu shots in August. The vaccine might not have been a perfect match for this year’s flu. And any protection we had probably has worn off by now.”

Flu cases jumped in April and May at the same time that Colorado has experienced a new wave of COVID-19 cases. You could call the convergence of flu and COVID-19 infections a “twindemic” of sorts.

“It’s the weirdest flu season I’ve ever seen,” said Barron, who is senior medical director of 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 are experiencing seasonal allergies as spring plants bloom. Those who are feeling sniffly or achy can’t be sure what’s making them sick unless they get tested for COVID-19 and the flu.

Typically, flu cases in North America peak during the winter months from December through February. This year, in Colorado’s most populous counties, flu cases began to climb in December, then dipped to uncharacteristically low levels in January and February. They then began to inch up again in March, and during April and May reached very high levels.

Barron sees a direct link between the end of COVID-19 mask mandates and the spring spike in flu infections.

“It has everything to do with COVID-19,” said Barron

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

On top of people not wearing masks in the spring, protection from fall flu shots also was decreasing.

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

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

During the winter months, Barron thinks people were wearing masks and being cautious while in crowded, indoor spaces.

“That probably suppressed the flu in the early months,” Barron said.

Then, politicians started lifting mask mandates. Many people were tired of worrying about COVID-19 and ditched their masks. And guess what? The influenza virus, which like all other viruses is opportunistic and finds hosts where it can, started spreading 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 flu could remain pervasive as COVID-19 infections continue to spread.

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

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

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

So, what should you do if you’re feeling sick?

Get tested, Barron advises.

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

“If you test negative for COVID-19, and you haven’t had exposure to people with the flu, you could be getting a false negative for COVID-19 or you could have the flu. The symptoms are similar: fever, body aches, cough,” Barron said.

Furthermore, a small number of people have gotten sick with both COVID-19 and the flu at the same time.

That kind of double whammy is not common, Barron said.

Nonetheless, it’s good to get tested. COVID-19 tests are available both at home and at health facilities. Please keep in mind that home tests are not as reliable as a nasal swab, PCR tests. With an at-home test, you can get false-negative results. So, if you’re feeling sick, be careful about exposing other people.

To get a flu test, contact your doctor’s office.

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

The antiviral medication 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 might also qualify to get additional treatments. It’s best to start these treatments within about five days of symptom onset.

As people cope with a crazy constellation of illnesses this spring, researchers are working on vaccines for the fall. Stay tuned for vaccine news throughout the summer. It’s possible that a combined vaccine for both flu and the newest COVID-19 strains will be available in the fall. If not, we could be in for another tough wave of multiple viruses.

“I’m seriously worried about the fall. COVID-19 likely will surge again. Our immunity will be suppressed and there could be new variants,” Barron said.

Thankfully, both vaccines and new treatments make flu and COVID-19 a little less dangerous.