Two new studies offer clues about which COVID-19 patients will go on to develop lingering symptoms known as long COVID.

The authors say their findings may help identify treatments to prevent these symptoms, which can include brain fog, fatigue, and shortness of breath, among other issues that can persist for months.

In one study, led by the Institute for Systems Biology in Seattle, researchers identified four factors that were associated with an increased risk of long COVID. They included a preexisting case of type-2 diabetes as well as three indicators that can be found in the person’s blood early in the course of disease:

  • Certain kinds of autoantibodies — an antibody that can attack the person’s own immune system.

  • High levels of RNA from the coronavirus.

  • The presence of DNA from another virus, called Epstein-Barr.

Patients with high levels of viral RNA — an indicator of “viral load” — might benefit from the prompt use of antiviral drugs, the authors wrote in the journal Cell.

Those with autoantibodies, whose immune systems can become overrun with abnormal inflammation, might benefit from certain anti-inflammatory medications. But the timing for such drugs can be tricky, lest they disrupt the type of healthy inflammation that is part of a normal immune response, the authors wrote.

Addressing the Epstein-Barr risk factor also may be a challenge. Most people have been exposed to that virus at some point, and it remains inactive in their bodies. But it becomes reactivated in some people when they are infected with the coronavirus, due to some type of “dysregulation” of the immune system, the authors wrote.

In the other study, researchers found that long COVID was more common in older COVID patients with a history of asthma and low levels of certain immunoglobulins (a type of antibody).

The authors of that study, published in Nature Communications, also said their findings could guide the way toward preventive treatments, but did not elaborate.

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Kartik Sehgal, a medical oncologist at Dana-Farber Cancer Institute in Boston who is studying long COVID, told NBC News that the findings are a valuable contribution.

If confirmed by others, the research is “an important step forward toward directing resources in post COVID-19 clinics to those who need them the most,” said Sehgal, who was not involved with the study.

More than one-third of COVID patients have reported experiencing “long” symptoms — typically defined as those present at least four weeks after the initial infection.

In both studies of long COVID, the authors did not break down their results by whether the participants had been vaccinated. Most of those in the Nature Communications study, led by scientists at the University of Zurich, in Switzerland, became ill before vaccines were available.

But as many physicians have pointed out, the vaccines likely are one of the best ways to prevent long COVID. A person can’t develop those lingering symptoms without becoming sick with COVID to begin with.

And even for those who get a breakthrough infection, the vaccines remain very effective at preventing severe disease.