The ‘twindemic:’ when flu season and spiking COVID-19 cases collide

Aug. 26, 2021
This scenic photo of mountains with ominous clouds represents an unknown scenario of a twindemic, what people are calling if COVID-19 infections and a bad flu season collide.
A “twindemic” could bring two pandemics at the same time: both flu and a bad wave of COVID-19 cases. The prospects of a twindemic are frightening, but we can prepare by getting vaccines for both flu and COVID-19. Photo: Getty Images.

By Clare Kavanagh and Katie Kerwin McCrimmon

What is a “twindemic” and how bad will it be?

If you haven’t heard the word “twindemic” yet, brace yourself. No, it’s not a post-apocalyptic flick about malicious twins raging during a pandemic. Rather, in a twindemic, we would face two pandemics at the same time: spikes in cases of COVID-19 and a simultaneous, rough flu season.

Last fall and winter, flu cases plummeted as fears of COVID-19 prompted people to isolate themselves, wash their hands frequently, avoid crowded indoor settings and religiously wear masks.

But this fall and winter could be entirely different. We could face a twindemic.

Why might there be a twindemic?

As many people got vaccines to protect themselves from COVID-19, they embraced freedoms, ditched their masks and launched into crowded settings. Meanwhile, the highly transmissible delta variant seized its opportunity to spread – primarily attacking unvaccinated people. Still, the newest wave of COVID-19 cases is worsening at a bad time of year.

Traditionally, annual flu cases hit hard in the late fall, exactly the time of year we’re approaching now, and in winter and early spring.

Whether or not we face a twindemic depends on how much worse the current wave of delta-stoked COVID-19 infections gets and what happens with the 2021-22 flu season.

“The truth is, we’re due for a flu pandemic. We have flu pandemics, on average, about every 10 years, so we are overdue,” said Dr. Michelle Barron, senior medical director of infection prevention and control for UCHealth.

“COVID-19 doesn’t count (as a flu pandemic),” Barron said. “It’s a novel, emerging infection that is completely separate from the history of flu pandemics.”

Headshot of Dr. Michelle Barron who answers the question: what is a twindemic?
Dr. Michelle Barron answers the question: What is a twindemic? Photo by Cyrus McCrimmon for UCHealth.

Despite Barron’s ominous observation, she cautions that flu is highly unpredictable. It’s quite possible that we could get lucky and have another year with fewer flu cases than usual.

Nonetheless, it’s her job to keep UCHealth patients, providers and staff members safe, so Barron has to prepare for the worst, including a twindemic.

To answer all of your questions about twindemics and other scenarios for fall and winter, we asked Barron what she’s expecting and how people can stay safe.

Barron has extensive experience leading the charge against infectious diseases including the last bad flu pandemic, H1N1 flu in 2009, along with Ebola in 2015, and, of course, the COVID-19 pandemic last year and this year. She’s also a professor of medicine and infectious diseases at the University of Colorado School of Medicine on the Anschutz Medical Campus. Barron is one of the top infectious disease experts in Colorado and also has coped with the loss of family members to COVID-19.

Here’s her key advice about a potential twindemic and staying healthy any time:

“Get the COVID-19 vaccine! Get the flu shot as soon as it is available. Wash your hands. Wear a mask.”

What is the flu?

The flu – or ­influenza as it’s formally known – is a group of viruses that cause respiratory infections. The flu can cause life-threatening complications. Because flu viruses are constantly changing, each flu season is different. That’s why we need to get annual flu shots.

Is the flu still a thing?

Yes. The flu is very much still a thing.

But it’s understandable that worries about COVID-19 might have made us temporarily forget about the flu. The 2020-21 flu season resulted in the fewest flu cases ever recorded, according to both the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC). The WHO and CDC have a collaborative research center that tracks flu cases over seasons. Researchers monitor weekly cases by geographic regions. They calculate and categorize breakout infections and predict trends in how infections will spread. To stay informed about flu cases, you can stay up to date by reviewing data through the FluSight program.

How can I stay safe against the flu?

Get your vaccines. (Annual flu shots should be available starting in September.) And take the same kinds of precautions you’ve been taking to stay safe from COVID-19.

Wash your hands frequently and thoroughly. If you’re sick, isolate yourself. Don’t spread your illness. If you have a cough, cover your mouth and wash your hands. Clean surfaces frequently that people share.

And, to stay well in general, Barron advises everyone to remember the basics: eat a healthy diet, get a good night’s sleep, get exercise and stay hydrated by drinking plenty of water.

The above symptoms are a compilation from the CDC’s comparison of cold and flu symptoms—click here to view—and the CDC’s comparison of flu and COVID-19 symptoms—click here to view.
The above symptoms are a compilation from the CDC’s comparison of cold and flu symptoms and the CDC’s comparison of flu and COVID-19 symptoms.  It can be difficult to tell the difference between a cold, flu and COVID-19. If you have any doubts, seek help from your medical provider and get tested for COVID-19. Graphic by Clare Kavanagh for UCHealth.

If I haven’t gotten my COVID-19 vaccine yet, is it OK to get the COVID-19 vaccine and my flu vaccine at the same time, or do I have to wait between shots?

Great question. Experts have done studies on exactly this topic and they learned that it’s fine to get multiple vaccines at the same time, Barron said.

“You can get the COVID-19 vaccine and any shots you need at the same time,” Barron said. “So, I’m not just plugging flu shots. I’m plugging everything. If you need a shingles shot, get your shingles shot. If you need your flu shot, get the flu shot. If you need your pneumonia shot, get your pneumonia shot.”

Is it also safe for children to get their COVID-19 vaccine when they get their flu shot or other vaccines?

So far, children and teens ages 12 and older can get COVID-19 vaccines. Clinical trials are underway now to test the COVID-19 vaccines on younger children, toddlers and infants, but those studies are not finished yet.

As parents of younger children eagerly await COVID-19 vaccines, it’s critical to keep up with all vaccinations for children.

“Yes! Kids need to get up to speed on whatever age-appropriate vaccines they’re supposed to have received,” Barron said. “We rely upon a high level of immunity in our community to stop the spread of these vaccine-preventable diseases.”

Some people report that they have gotten the flu shot in the past and still got sick. Does the flu shot work? If it works, why do people still get sick?

“The flu vaccine decreases the severity of illness and reduces the likeliness of hospitalization. Flu shots are not perfect. Imagine it as a horse race. Experts are betting on which strain will win and will be the most aggressive, but there’s no perfect betting in horse races,” Barron said.

In other words, vaccine makers have to make educated “bets” on which strains of flu will be bad during the next flu season. Then they formulate flu shots that they hope will protect us. Sometimes they bet well. Sometimes they don’t guess as well. In a good year, the flu vaccine will be about 60% effective in preventing flu infections. While the flu shot is not perfect, it will help decrease the severity of illness of the flu and it will help you stay out of the hospital and prevent you from dying, Barron said.

Should I get my flu shot even though it doesn’t work 100% of the time?

Most definitely.

“Some people say, ‘why bother getting the vaccine?’ But, what in life is 100% guaranteed? The only thing we can predict with 100% guarantee is that we know we will die someday,” Barron said. “For me, not getting hospitalized and not dying from the flu or other vaccine-preventable diseases are two good things in my mind.”

Should we be wearing masks during the flu season in order to prevent a twindemic?

Yes, it’s wise for anyone who is vulnerable to wear a mask and medical workers and many others — like those working at airports — are required to do so, Barron said.

“Health care workers in departments with immunocompromised patients, such as the cancer ward, have worn masks during flu season for years,” she said. “Is it necessary right now? Yes. We are at war with COVID-19. It is naïve to think the worst (COVID-19 spike) was this summer.”

Barron encourages healthy members of the public to do all they can to prevent critical illnesses so hospital workers care for everyone who needs help.

“Wear a mask. Get vaccinated. Get the flu shot as soon as it is available. Health care workers are exhausted and spread thin, so if that is the motivation needed, get vaccinated and wear masks for the front-line workers who have been battling the COVID-19 pandemic for 18 months.”

She compares vaccines and masks to seat belts and air bags in cars.

“Nothing works 100% of the time. We have all of these layers of protection. I use the analogy of a car, like wearing your seat belt, having airbags and driving the speed limit. Are any of them guaranteed to keep you safe if you have an accident? No, but if you get in a crash, it sure is nice to have all three,” Barron said.

Should children wear masks?  

“There are definite health benefits to kids and teens wearing masks. Understandably there also are concerns about psycho-social development. However, my own niece actually feels safer wearing a mask. The comfort level of each child varies, but the evidence about education is clear that students are performing better in-person, and masking can help keep them attending school in-person,” Barron said.

Who is most likely to get the flu?

“The extremes in age — our youngest and oldest people — are most likely to get sick with the flu. Children under 5 years old and adults over 65 are most likely to get severely ill and hospitalized with the flu,” Barron said.

What can we learn from last year’s flu season?

Because of fears about COVID-19 last year, a record number of people got flu vaccines last year.

“The flu vaccination rate last year was the highest Colorado has ever seen,” Barron said.

She hopes the trend continues this fall and winter.

Barron attributes the low number of flu cases to the high vaccination rate and preventive measures that people took seriously, like social distancing and mask wearing.

Flu deaths were also much lower last year in the U.S. than in previous years, with just one pediatric flu death during the 2020-21 flu season compared to at least 199 pediatric flu deaths previous year.

Can the flu cause hospitalizations and deaths?

Yes. The flu can be very dangerous, Barron said.

Even in relatively mild flu years, influenza has a big impact. Before most people started taking precautions related to COVID-19, the 2019-20 flu season left an estimated 38 million sick, led to 405,000 hospitalizations and 22,000 deaths in the U.S., according to CDC experts.

The 2009 flu season was extremely severe, and unlike some years, that flu strain attacked young people.

“Twenty-year-olds were on ventilators and prone,” Barron said. “I still have nightmares about the 2009 flu.”

Do you think we will have a twindemic?

There is no way to predict how bad the flu season will be, Barron said.

She jokingly picks up a Magic 8 Ball from her desk, shakes it and sees what random answer the toy gives.

“We make all of these predictions, but something can come out of left field. We don’t have control over all of the variables,” Barron said.

Her philosophy is to be as prepared as possible.

“We are planning ahead for the worst-case scenarios and doing everything we can to be prepared,” Barron said.

When should I get my flu and COVID-19 shots?

Get your COVID-19 vaccine now if you have not done so already. There are plenty available. And, schedule your flu shot as soon as the vaccines become available. You can actually get your COVID-19 and flu vaccines together if that is more convenient.

“Get your flu shot early,” Barron said. “Get it as soon as it’s available. Get if off your to-do list. This is one to check off immediately. Don’t wait until December.”

If we have a twindemic, how will I know if I have the flu or COVID-19 this year?

Some symptoms of flu and COVID-19 are very similar, such as a fever, cough and body aches. Learn more about how to evaluate your symptoms.

Could we get a novel strain of a flu virus like we did with the novel coronavirus?

Yes, that’s possible.

That’s the kind of scenario that keeps Barron up at night.

“The question would be, ‘How bad is this flu strain?’ Is it like the 1956 flu or the 1918 flu? Do we have immunological reserves against it?” Barron said. “COVID-19 has been so severe because we had no natural immunities to it.”

Of course, Barron and all other infectious disease experts are hoping for another mild flu season. One pandemic has been more than enough to cope with. Skipping a twindemic would be ideal.

Finally, how can people deal with the anxiety of worrying about a twindemic?

“Get vaccinated. Wash your hands. Wear a mask and get a good therapist,” Barron says with a laugh. “Or take up kickboxing or get a dog.”

About the author

UCHealth is an innovative, nonprofit health system that delivers the highest quality medical care with an excellent patient experience. With 24,000 employees, UCHealth includes 12 acute-care full-service hospitals and hundreds of physicians across Colorado, southern Wyoming and western Nebraska. With University of Colorado Hospital on the Anschutz Medical Campus as its academic anchor and the only adult academic medical center in the region, UCHealth pushes the boundaries of medicine, providing advanced treatments and clinical trials and improving health through innovation.

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