Do I Have the ‘Super Flu’? Here’s What You Need to Know

This winter is playing host to an especially bad flu season in the United States—one that might leave you with plenty of worries and questions.

Perhaps the most pressing concern, especially for those of us starting to feel under the weather, might be: how do you know when you’re sick with the flu, or even the so-called “super” flu?

Cold vs flu

There are many germs out there that can cause respiratory illness. That said, most of these tend to be viruses.

What we call the common cold is actually an assortment of many viruses—over 200 in total—that can all cause a respiratory infection. The flu, meanwhile, is only caused by the influenza virus, though there are many different types of influenza circulating around the world at any given time (including influenza viruses that usually sicken other animals, like birds).

Though colds and flus do share some similarities, there are real differences between them.

Colds are generally upper respiratory infections, meaning they’re isolated to your nose, throat, and sinuses. They usually cause symptoms like a runny or stuffy nose, sore throat, cough, and sneezing. Miserable as a cold can feel, these symptoms tend to gradually develop, are relatively mild in intensity, and clear up within a week.

Typically, flus also cause upper respiratory infections. But as anyone who’s had it can tell you, the flu often hits harder and more abruptly than a cold. So your throat might feel especially raw if you have a flu. The flu also commonly causes systemic symptoms like fever, body aches, and fatigue. And a flu will stick around longer on average, sometimes up to two weeks. Flu is also more likely to spread deeper into the lower respiratory tract, where it can trigger more severe and even life-threatening complications like pneumonia and bronchitis.

There are nuances to all this. Some germs, like the respiratory syncytial virus (RSV), can cause a cold in most people but are more likely to cause severe illness in vulnerable groups like very young children than others, for instance. And even generally mild cold viruses can occasionally cause lower respiratory infections.

As a general rule, though, if your respiratory illness isn’t knocking you completely off your feet, you’re probably not having the flu.

What about the super flu?

This flu season is being driven by a particular variant of H3N2 flu, known as subclade K.

H3N2 flus tend to cause a bit more misery than other seasonal flu viruses. But K is all the more worrying because it emerged unexpectedly last year and is noticeably different on a genetic level from the strains that scientists predicted would be circulating right now. As a result, the seasonal flu vaccine is mismatched to K, reducing its effectiveness.

The good news is that K isn’t appearing to cause more severe illness on average than other H3N2 viruses. But its arrival does seem to have fueled unusual waves of flu around the world. In some countries like Australia, it prolonged the flu season; in others like the UK, it helped start the season earlier. And in the U.S., it’s contributed to record levels of flu this winter.

Data from the Centers for Disease Control and Prevention released Monday shows that doctors’ visits for flu-like illness last week were the highest ever recorded in the country since modern tracking began almost 30 years ago. The CDC also estimates that the flu has sickened 11 million people, hospitalized 120,000, and killed 5,000 so far this season. And it’s likely that flu activity will remain high for several more weeks at the very least.

Many flu diagnostic tests, either the kind you get at your doctor’s office or take at home, will identify the broad type of influenza you have (A or B). Some might even identify the strain, such as H3N2. Scientists can also conduct further testing to diagnose a specific variant, but these results are used by local and federal health officials to track flu trends and aren’t widely available to the public.

Given that and the fact that subclade K isn’t worse than the average flu, you’ll probably never know for sure if K is to blame for your flu infection. That said, the chances are pretty good it is.

According to the CDC, nearly all tested samples reported last week by public health labs came back positive for H3N2 (91%). And of all the H3N2 samples further tested by the CDC since last September, about 90% were identified as subclade K.

Mismatched as it is to subclade K, the flu vaccine is still providing some level of protection against seasonal flu, data from the UK has shown. So it’s still worthwhile to get your shot. Other precautions like regularly washing your hands and wearing masks can lower your risk of catching the flu as well.

Best of luck out there.