Acute symptoms of COVID-19, such as cough, fever and shortness of breath, are now widely known. What is not known, however, is what symptoms and complications may linger long after an initial COVID-19 infection. Early research shows the disease attacks more than just the respiratory system, affecting multiple organs with blood clots and inflammation.

"This is a disease that has a number of mysteries involved, compared to the usual respiratory virus," says Dr. Gregory Poland, a COVID-19 expert at Mayo Clinic. "On the one hand, we see very severe but variable manifestations. On the other hand, (we see) infection without symptoms. We also see a diminution of immunity over time with this coronavirus."

What's just starting to emerge, according to Dr. Poland, is this idea of COVID-19 "long-haulers," which is a term used to describe people who develop long-term and ongoing complications.

"We're really seeing a number of reports of people who report long-term fatigue, headaches, vertigo (and), interestingly enough, difficulties with cognition, hair loss, cardiac issues, and diminished cardiorespiratory fitness. And I think what we're going to find out is that a large portion ― not all, but a large portion of that ― is likely to relate to the significant cellular-level damage that this virus can cause," says Dr. Poland.

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Some of the possible long-term effects can affect even patients who are asymptomatic or have mild cases of COVID-19.

"I think it's an argument for why we take this disease so seriously," says Dr. Poland. "People who are thinking, especially young people: '(It's a) mild disease, you know. I might not even have any symptoms, and I'm over it.' Whoa. The data is suggesting otherwise. There's evidence of myocardial damage, cardiomyopathy, arrhythmias, decreased ejection fractions, pulmonary scarring and strokes.

"And then in the more acute phase, extending out for a month or two, has been this really interesting issue of coagulation abnormalities, which have been responsible for both small-vessel and large-vessel arterial and venous occlusions. So this can be a really wicked virus in some people," says Dr. Poland.

"We're going to see more and more of the longer-term consequences come out, and we're going to need to study those as vigorously as we did the acute symptoms. Catalog them, understand them and then do clinical trials to figure out how best to treat them," says Dr. Poland.

Check the CDC website for additional updates on COVID-19. For more information and all your COVID-19 coverage, go to the Mayo Clinic News Network and mayoclinic.org.