For many people who contract mild, moderate, or severe COVID-19, the disease's effects don't disappear when the infection fades. A systematic review and meta-analysis published Monday to the journal Scientific Reports found that 80% of cases result in at least one long-term symptom.

The authors of the report scoured more than 18,000 publications, seeking studies assessing the long-term effects of COVID-19 with at least 100 subjects. They found fifteen studies, which collectively followed 47,910 patients for as long as 110 days post-infection. They then pooled the data to discern the prevalence of chronic side effects.

"The five most common symptoms were fatigue (58%), headache (44%), attention disorder (27%), hair loss (25%), and dyspnea [difficult breathing] (24%)," the reviewers reported.

In total, they turned up 55 potential long-term symptoms. Other notable chronic effects included loss of taste (reported in 23% of cases), loss of smell (21%), cough (19%), sweating (17%), and hearing loss (15%).

Lopez-Leon et al. / Scientific Reports

Unfortunately, none of the studies included in the review were stratified by disease severity, so we don't know for sure if worse disease exacerbates long-term symptoms, though it seems likely.

"The results assessed in the present study are in line with the current scientific knowledge on other coronaviruses, such as those producing SARS and MERS," the authors wrote. "For example, studies on SARS survivors have shown lung abnormalities months after infection."

The authors also noted that the effects of long-term COVID-19 partly resemble those of chronic fatigue syndrome (CFS), a nebulous, controversial diagnosis that currently lacks an established cause. CFS sufferers are plagued by "severe incapacitating fatigue, pain, neurocognitive disability, compromised sleep... and worsening of global symptoms following minor increases in physical and/or cognitive activity," the reviewers described.

It's uncertain why some COVID-19 patients experience long-term effects. Genetics, age, route and dose of infection, and inflammation levels could all play a role, the authors said.

"Given that COVID-19 is a new disease, it is impossible to determine how long these effects will last," they added.

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