OHSU study suggests long COVID may be more common than previously thought

New research from Oregon Health & Science University suggests that long-term effects of COVID-19 may be far more common and slower to appear than previously believed.

In a study published last week in PLOS Pathogens, scientists tracked a group of rhesus macaques infected with the delta variant of the coronavirus. The animals, all unvaccinated and previously unexposed to the virus, appeared to recover quickly.

But over six months, researchers found signs of chronic health issues in most of them — despite their initial symptoms being little more than sniffles.

“You don’t have to have a very severe case of COVID in the first place to have potentially long-term changes,” said Dr. Charles Roberts, a lead author of the study and professor at OHSU’s Oregon National Primate Research Center.

Although the animals showed only mild symptoms during the acute phase of infection, up to 90% developed signs of chronic health issues months later — including inflammation, disrupted sleep and changes in metabolic hormone levels tied to conditions like diabetes and heart disease.

The idea isn’t new to people suffering from long COVID, the umbrella term for symptoms that persist or appear long after someone has technically recovered. Fatigue, brain fog, and insomnia are among the most commonly reported problems.

But estimating how many people are affected has been tough, since previous studies have largely relied on self-reported symptoms and inconsistent diagnostic criteria, Roberts said. The study’s findings suggest that those effects may be much more widespread than previously thought.

“Some adverse aspects of long COVID may not be apparent until some point in the future,” he said. “That suggests the condition could be more common than current estimates reflect.”

The researchers were interested in how the virus that causes COVID-19 interacts with metabolic health. Roberts, who spent a decade studying diabetes and obesity at the National Institutes of Health, said the team wanted to explore what he called a “reciprocal relationship” between COVID-19 and chronic conditions.

“If you had already had metabolic disease, like obesity, diabetes or hypertension, that meant that if you got COVID, it was going to be worse,” he explained. “On the other hand, there was a potential risk of new-onset metabolic disease after COVID.”

To test this, the researchers used rhesus macaques at OHSU’s Oregon National Primate Research Center. The Hillsboro facility has long been the target of animal rights groups, who have raised concerns about disease, lab conditions and the ethics of animal studies. OHSU has maintained that most primates live in outdoor social groups, receive attentive veterinary care, and are part of research that meets strict federal standards.

Roberts said rhesus macaques serve as a close biological proxy for humans and a proven model for studying infectious diseases. Primates, he said, offer a controlled system that lets scientists “track things you just can’t see in people.”

The study observed the animals in two groups — some lean and healthy, others overweight — to see how underlying health influenced long-term effects.

While the overweight animals experienced more dramatic changes, even the lean, healthy group didn’t fare much better. In some cases, the leaner animals saw persistent internal disruptions that made them resemble unhealthier, obese animals.

Roberts said the study helps validate the experiences of patients and expands scientific understanding of how a seemingly short illness may ripple through the body long after the virus is gone.

And another key takeaway, Roberts said, is that people who had mild symptoms of COVID-19 should not ignore symptoms that crop up later.