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Have you ever had a cold you just couldn’t shake for weeks—one that definitely wasn’t COVID?

“Long COVID”—lingering symptoms after a SARS-CoV-2 infection that can last for weeks, months, or even years—is a thing.

“Long cold” may be a thing, too.

That’s according to a new study released Friday by Queen Mary University of London, published in The Lancet’s EClinical Medicine. Researchers asked hundreds of recently ill patients who had been recovering for four weeks or longer what symptoms they were experiencing. Some had recently had COVID, and others had recently had one of a number of other another acute respiratory infections, which researchers generalized as a “cold.” Those conditions included:

• Pneumonia

• Flu

• Bronchitis

• Tonsillitis

• Pharyngitis

• Ear infection

• Common cold

Some of the most common symptoms in patients who had recently experienced an acute respiratory infection included:

• Cough

• Stomach pain

• Diarrhea

And some of the most common symptoms in patients who had recently experienced COVID included:

• Problems with taste or smell

• Lightheadedness or dizziness

Otherwise, the lingering symptoms of both were largely the same, and included:

• Stomach problems

• Muscle or joint pain

• Sleep problems

• Memory problems

• Difficulty concentrating

“Our findings shine a light not only on the impact of long COVID on people’s lives, but also other respiratory infections,” Giulia Vivaldi—a statistician and epidemiologist at Queen Mary University of London and lead researcher on the study—said in a news release about it. “A lack of awareness—or even the lack of a common term—prevents both reporting and diagnosis of these conditions.”

“As research into long COVID continues, we need to take the opportunity to investigate and consider the lasting effects of other acute respiratory infections.”

Those who are more severely ill during their infection tend to more frequently report long-term symptoms. Otherwise, research is ongoing to figure out just why some develop “long” illnesses and others don’t.

Post-viral illnesses share similarities

Long COVID is a post-viral illness that occurs after infection with COVID. Also known as PASC, or post-acute sequelae of COVID, it’s typically defined as new symptoms that develop after infection and persist for at least four weeks—often for months, and sometimes for years.

Similar post-viral illnesses can occur with other viruses, too, like the flu, herpes, Lyme disease—and even Ebola and SARS. Post-viral illnesses often have a chronic fatigue syndrome-like presentation, with symptoms like fatigue, brain fog, and post-exertional malaise, in which symptoms get worse after mental or physical activity.

Post-viral illness from the flu and long COVID seem to occur at similar rates, according to research presented this spring at the European Congress of Clinical Microbiology & Infectious Diseases in Copenhagen, Denmark. For 12 weeks, researchers followed thousands of adults with lab-confirmed flu or COVID. Twelve weeks out, 21% of those who had been sick with COVID had continuing symptoms, and 23% of those had been sick with the flu did as well. In both groups, 4% of participants had severe symptoms that they said impacted their daily lives. Long COVID is reportedly more common because COVID is more common than the flu, researchers concluded.

Some experts speculate that at least some long COVID cases are the result of the SARS-CoV-2 virus reactivating reservoirs of other viruses a person has previously battled, potentially leading to symptoms of chronic fatigue syndrome, according to an October 2022 study published in the journal Frontiers in Immunology. Researchers found herpes viruses like Epstein-Barr, one of the drivers behind mono, circulating in patients who had experienced COVID. In patients with chronic fatigue syndrome, antibody responses were stronger, signaling an immune system struggling to fight off the lingering viruses.

Pathogens like Epstein-Barr virus have been named as likely culprits behind chronic fatigue syndrome, also known as myalgic encephalomyelitis.