Why some people can recover from COVID-19 relatively unscathed but others are affected by lingering long-COVID symptoms is being uncovered by new research. 

As per the study, reported in the journal Cell, there are four key factors that appear to be linked to a higher risk of experiencing long-COVID:

• how high the viral load is during the opening stages of the infection.
• the presence of certain autoantibodies.
• pre-existing Type 2 diabetes.
• patients with reactivated Epstein-Barr virus in their blood – the pathogen that causes glandular fever, also known as infectious mononucleosis or “mono.” 

A huge team of scientists from across the US reached these findings by collecting blood and swab samples from over 300 COVID-19 patients during the initial phase of their infections, then two to three months later.

Using these four factors, the researchers gained a solid idea of a person’s chances of developing long-COVID, which they refer to as Post Acute Sequelae of COVID-19 (PASC).

"Identifying these PASC factors is a major step forward for not only understanding long COVID and potentially treating it, but also which patients are at highest risk for the development of chronic conditions," Dr Jim Heath, co-corresponding author and President of the Institute for Systems Biology, said in a statement.

“These findings are also helping us frame our thinking around other chronic conditions, such as post-acute Lyme syndrome, for example," he added. 

Researchers are still trying to get their heads around long-COVID and there are still many unknowns surrounding the condition. It generally refers to a wide array of new, returning, or ongoing health problems people can experience four or more weeks after first getting COVID-19.

These hundreds of documented symptoms can range wildly, including breathlessness, fatigue, headaches, brain fog, achy muscles, sexual dysfunction, visual hallucinations, tremors, itchy skin, changes to the menstrual cycle, heart palpitations, bladder control issues, shingles, memory loss, blurred vision, diarrhea, and tinnitus.

Estimates vary, but most research indicates that somewhere between 3 to 12 percent of people infected with COVID-19 have symptoms 12 weeks after the initial infection. Considering hundreds of millions of people have caught the virus globally, that’s a hell of a lot of people. 

One of the big questions is how to treat long-COVID. There are no certain answers yet, but evidence is emerging that vaccination can help ease many (but not all) symptoms of the condition. The researchers on this study are yet to fully explore their data, but they hope their findings might inform future strategies to tackle this growing public health concern. 

“Long COVID is causing significant morbidity in survivors of COVID-19, yet the pathobiology is poorly understood," explained Dr Jason Goldman, co-corresponding author of the paper and an infectious disease expert at Swedish.

"Certain findings such as the low cortisol state in patients with long COVID have potential to translate rapidly to the clinic. Our results form an important foundation for the development of therapeutics to treat long COVID."