This winter is seeing a notably severe flu season across the United States, which may leave many feeling anxious and with numerous questions.
A key concern, especially as some of us begin to feel unwell, is figuring out whether it’s the flu or even the so-called “super” flu.
Differences Between Cold and Flu
There are a lot of germs that can lead to respiratory illnesses, and most of them are indeed viruses.
The common cold is actually a mix of various viruses—over 200 different ones can cause respiratory infections. On the other hand, the flu is specifically due to the influenza virus, though different strains circulate globally, including some that usually infect animals such as birds.
Colds and flus have some things in common, but there are distinct differences worth noting.
Colds typically affect the upper respiratory system, meaning they target your nose, throat, and sinuses. They bring symptoms like a runny or blocked nose, sore throat, cough, and sneezing. While colds are indeed uncomfortable, these symptoms tend to develop gradually, are relatively mild, and usually resolve within a week.
Flus, while also causing upper respiratory issues, often hit harder and more suddenly than a cold. If you have the flu, your throat may feel particularly sore. Common systemic symptoms include fever, body aches, and fatigue, and the flu can linger longer—sometimes up to two weeks. Moreover, it is more prone to infiltrate the lower respiratory tract, leading to more severe complications like pneumonia and bronchitis.
Of course, there are exceptions. Some viruses, like respiratory syncytial virus (RSV), typically cause a cold in most individuals but can result in serious illness for vulnerable populations, such as young children. Even mild cold viruses can occasionally lead to lower respiratory infections.
As a general guideline, if your respiratory symptoms aren’t completely knocking you down, it’s likely not the flu.
Understanding the Super Flu
This season’s flu outbreak is primarily being driven by a specific variant of H3N2, referred to as subclade K.
H3N2 strains often bring about a higher level of discomfort compared to other flu viruses, and K is concerning because it unexpectedly emerged last year and is genetically different from the strains anticipated to be circulating currently. This mismatch has rendered the seasonal flu vaccine less effective.
On a positive note, though, data indicates that K doesn’t appear to cause more severe illnesses than other H3N2 strains. However, its emergence has led to unusual flu patterns worldwide—some countries like Australia experienced prolonged flu seasons, while others, including the UK, saw an earlier onset. Here in the U.S., K has contributed to unprecedented flu levels this winter.
The Centers for Disease Control and Prevention (CDC) released data showing that visits to doctors for flu-like illnesses were at a record high last week—unprecedented in nearly 30 years of tracking. The agency estimates that 11 million people have been infected, 120,000 hospitalized, and 5,000 have died this season, with flu activity expected to remain elevated for several more weeks.
Many flu diagnostic tests available at medical offices or even for at-home use can identify whether you’ve contracted influenza A or B, and some can pinpoint the strain, like H3N2. Further testing can identify specific variants, but these results are generally used for epidemiological tracking by health officials rather than being available to the public.
Considering all that and the fact that subclade K is not more severe than typical flu variations, it’s likely you might never know if K is responsible for your flu illness. However, it seems reasonable to think it probably is.
The CDC reports that nearly all recently tested samples—about 91%—came back positive for H3N2. Of the H3N2 samples tested since last September, roughly 90% were identified as subclade K.
Despite its mismatch with subclade K, the flu vaccine still offers some level of protection against seasonal flu, as shown by data from the UK. So, it remains beneficial to get vaccinated. Additionally, practices like washing your hands often and wearing masks can help reduce your risk of catching the flu.
Wishing you the best of luck this season.
