When Influenza and COVID-19 Collide

With similar symptoms, the two viruses are hard to distinguish and all to easy to misdiagnose. The difference is, one of them can be prevented.

For several decades, we’ve had a protective vaccine against the flu. For most of us, it’s a no brainer. Of course, we’ll get the flu shot. Why bother suffering through fever, chills, headaches or complications like pneumonia. This year, though, the stakes are a lot higher.  

As we struggle with COVID-19, do we really want the risk of co-infection of flu and SARS-CoV-2?   

Differences Between Influenza and COVID-19

We know a lot more about the flu than we do about SARS-CoV-2, which is a new human pathogen. But we are starting to understand more about how they differ. 

Both can cause fever, sore throat, runny nose, cough, trouble breathing, muscle aches, headache, and fatigue, but COVID-19 might also manifest as a change in or loss of taste or smell. Infection with influenza causes symptoms within four days, whereas it can be up to 14 days with SARS-CoV-2.

Both viruses spread the same way, but COVID-19 is more contagious – spreading quickly and easily to a lot of people – than the flu. Thus superspreader events. 

Most people recover from the flu within two weeks. It’s not entirely clear how long it takes for COVID-19 because there is so much variability and many lingering symptoms. 

Both can have complications, but with COVID-19, there are additional problems with the lungs, brain, and blood clots and a multisystem inflammatory syndrome in children.

But one of the biggest differences is therapy – we have a protective vaccine only for the flu and well-established, effective antiviral drugs like Tamiflu for severe cases of the disease. For COVID-19, all this is in the future. 

When Two Infections Collide

We don’t yet know enough about COVID-19 to be sure what will happen when someone is infected by both viruses at the same time. We do know that the two have similar symptoms and will be tough to distinguish, which means that people will need to get tested for both. 

Some people with flu get severely ill and need hospitalization – which we expect and which could increase their risk of catching COVID-19. Having the flu and COVID-19 at the same time could easily make us sicker, and increase the number of people needing hospitalization and intensive care beds. That means that patients with both infections could strain the system and lead to unnecessary deaths. 

What we really don’t know is whether co-infection could make mild cases of the flu and COVID-19 more prone to complications and death or whether one virus might reduce the chances of catching the other.  then again, do we want to take the risk?

Protection Against Two Simultaneous Pandemics

Because influenza and SARS-CoV-2 viruses spread in the same way, your newly-acquired anti-COVID-19 habits – avoiding crowds, wearing a mask, keeping physical distance, cleaning your hands, keeping your hands away from your face and self-isolating if you’re sick – will work for flu too. 

BUT: Get a flu shot! The flu vaccine typically protects about 70% of people. But even if it’s not perfect, it will significantly reduce the number of flu cases. 

Optimally, everyone over six months old should get a flu shot. However, it’s especially important for pregnant women, people over 65, healthcare workers and people with underlying conditions such as diabetes, high blood pressure or lung disease, who are at risk of developing serious complications. 

There are exceptions: Anyone with severe allergies to a flu vaccine or its ingredients, or with a previous history of Guillain-Barré Syndrome. If you’re uncertain, check with your doctor first. Beware that there is always a limited number of vaccines. So, if you’re in a high-risk group, get vaccinated as soon as the vaccines become available.

Let’s Be Proactive This Flu Season

Do we really have to worry about getting the flu this year, when fewer people are travelling, and we have measures in place for slowing the spread of COVID-19?

It’s a good question: There is a chance that we might have less flu this year under these conditions. But with the recent increase in COVID-19 cases, nothing is certain. 

My advice: Don’t take a chance.

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Dr. Michelle Epstein
Michelle Epstein is a medical doctor graduated from the University of Alberta in Canada, who has specialised in Internal Medicine at the University of British Columbia and Allergy and Clinical Immunology at Yale University. Since 2004, she has been a Lab Leader at the Medical University of Vienna’s Division of Immunology.

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