You’ve heard of “long COVID,” but COVID isn’t the only illness that can cause lasting symptoms. Other respiratory infections, including colds, flu, and pneumonia, seem to sometimes trigger a “long” version as well.
This may not be shocking news if you’ve ever noticed a cough or body aches sticking around for some times after you otherwise feel recovered from a cold or flu. But the phenomenon hasn’t been a well-studied until recently. As scientists try to understand long COVID, they’re beginning to learn about “long” forms of other illnesses.
What are the symptoms of long colds and long flu?
A new study on long COVID compared people who had had COVID infections with those who had other respiratory infections (like a cold) alongside a negative COVID test. The researchers’ aim was to figure out how long COVID differs from these other illnesses.
The study looked at surveys of people in the United Kingdom from January 2021, after COVID had been circulating for a while but before most of their volunteers had gotten the vaccine. To distinguish long COVID from other post-infection syndromes, they asked about other infections, as well as cases of the coronavirus.
“Long cold” is a term that comes from the press release announcing this paper, but these non-COVID infections weren’t just colds. They included “pneumonia, influenza, bronchitis, tonsillitis, pharyngitis, ear infection, common cold, or other upper or lower respiratory infection not caused by SARS-CoV-2,” which means that the researchers looked at potentially life-threatening cases of, say, pneumonia alongside ordinary colds. Which is to say, it’s a big group. So, yes, long colds were included in this research, but they were included alongside what you might call “long pneumonia” and more.
The study found that COVID and other respiratory infections could result in a similar “long” syndrome in the four to 12 weeks after the initial illness. (That’s just the timeframe they studied; the actual length of symptoms could have been longer). Symptoms for both long COVID and “long colds” include:
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Muscle and joint pain
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Trouble sleeping
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Difficulty concentrating or remembering things
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Lightheadedness and dizziness
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Coughing
People with long COVID were more likely to have impaired smell or taste; that wasn’t as common with other respiratory infections. They also reported more lightheadedness and dizziness.
Are “long cold” and “long flu” real?
“Long cold” and “long flu” aren’t commonly recognized terms—yet—but the idea that symptoms can linger after an infection is not new. A 2022 paper called post-infection syndromes a, “significant blind spot in the field of medicine.” We do know that cases of myalgic encephalomyelitis or chronic fatigue syndrome (ME/CFS) can be preceded by infection; there is hope that research into long COVID can benefit people who have ME/CFS as well.
But when people get diagnosed with ME/CFS, they tend to have fairly severe symptoms. The attention to “long COVID” as its own syndrome has meant that people are paying more attention to lingering symptoms that follow even mild or moderate infections, or when the symptoms themselves are not severe but are long-lasting.
And, as a result of that attention to long COVID, the investigators in the recent Lancet paper found themselves needing to ask what symptoms people have after other infections, to distinguish those from long COVID. They found plenty of similarities between the two, suggesting that “long colds” have flown under the radar for some time, alongside what we might call “long flu,” “long pneumonia,” and others.
It’s important to note that the new study has limitations in its comparison of long COVID with the other syndromes. Diagnosis was largely self-reported, and a person who had COVID but got a false negative on a COVID test would have been lumped in with the “other” infections. (Critics have also questioned whether comparing “long COVID” to “long colds” minimizes or belittles patients’ experiences with severe long COVID; I don’t agree with that framing, but I do think it’s important to note that these non-COVID infections and their post-infection symptoms are not necessarily mild.)
Still, we are learning more about how the human body can react after an infection, and that’s a field that deserves more study. The researchers of the recent paper write:
A lack of awareness of post-acute sequelae of other [acute respiratory infections]—or even the lack of a common term, like ‘long COVID’—is likely to contribute to under-reporting.
If that’s true, simply giving “long colds” a name is a step towards understanding them better.
