Just what is Long COVID?

More than two years into the pandemic, scientists have yet to come to a consensus.

It seems like most any ailment—from the expected, like fatigue, dry cough, and shortness of breath—to the obscure, like ear numbness, a sensation of "brain on fire," and hallucinations—could be symptoms, according to a landmark July study published in British medical journal The Lancet.

In fact, the study identified more than 200 potential Long COVID symptoms in 10 organ systems, with 66 symptoms typically lasting over seven months. Researchers surveyed nearly 4,000 sufferers with confirmed or suspected COVID from nearly 60 countries, with illness of a month or longer.

Now, a new study out of Italy, published earlier this month, found that symptoms of Long COVID may vary based on the variant. When researchers examined the records of nearly 450 patients, they found that those infected with the Alpha variant, the first identified COVID variant of concern, were more likely to experience muscle aches, insomnia, brain fog, and anxiety or depression when compared to patients with the initial strain of COVID—and less likely to experience the stereotypical loss of taste or smell.

Victims of childhood trauma are more likely to develop Long COVID, according to a not-yet-peer-reviewed study published in February to preprint server medRxiv—likely due, researchers say, to altered immune response.

The World Health Organization defines Long COVID as a condition that occurs in someone who had COVID, with symptoms that cannot be explained by another diagnosis, that last for two months or more. The symptoms can persist following the initial onset, or come and go over time, the organization says, adding that a diagnosis of Long COVID usually wouldn't be made until three months after acute illness.

However, the Mayo Clinic defines Long COVID as a set of symptoms stemming from COVID that persist for more than four weeks after diagnosis.

An estimated 10%-30% of individuals who have COVID will experience Long COVID based on the Mayo Clinic’s definition, the American Medical Association points out—even if they never felt sick when they contracted the virus.

The Lancet study lists a dizzying array of symptoms. Among the most common: fatigue, elevated temperature, extreme thirst, menstrual issues, heart palpitations, rapid heartbeat, tightness in chest, muscle aches, joint pain, worsening allergies, sore throat, blurred vision, shortness of breath, dry cough, diarrhea, loss of appetite, frequent headaches, altered taste/smell, and itchy skin.

And those were just the physical symptoms.

Frequent mental symptoms included anxiety, irritability, insomnia, brain fog, memory loss, and difficulty finding the right words. Also reported: suicidality, delusions, inability to yawn, inability to cry, sensation of "brain warmth/on fire," ludic dreams, sleep apnea, inability to record new memories, speaking unrecognizable words, and hallucinations.

Those with long COVID experienced an average of 60 symptoms in nine organ systems over nine or more months before recovering, if symptoms ever subsided. At the seven-month mark, many Long COVID patients were still suffering and hadn't returned to previous levels of work, the study found.