The novel coronavirus could be playing hide and seek in the body, causing people to suffer long-term symptoms. This is what scientists are eager to validate in an effort to understand long COVID and come up with ways to deal with the condition.

There appears to be mounting evidence to support the idea that virus reservoirs in the body, especially in the gut, could be the reason why some people continue to experience symptoms months after battling the infection.

Professor David R. Walt and his colleagues at Harvard Medical School announced earlier this month that they detected SARS-CoV-2 proteins in the blood of 65% of long COVID patients up to 12 months since their bout with the virus. The study may be small in scale, but it does provide compelling evidence to the idea that virus reservoirs could be causing the long-term illness.

“The half-life of spike protein in the body is pretty short, so its presence indicates that there must be some kind of active viral reservoir,” Walt was quoted as saying by The Guardian on Tuesday.

Spike protein was not detected in the blood of COVID patients who did not have long-term symptoms. This would suggest that the protein could be responsible for the lengthened manifestation of symptoms in long COVID patients.

Previous research led scientists to uncover COVID virus genetic material in stool samples of patients, particularly kids with multisystem inflammatory syndrome. Treating the patients with a drug that reduced intestinal permeability caused the rapid clearance of the material in stools and improved their condition. Walt hypothesized that something similar could be happening in long COVID patients.

Meanwhile, PolyBio Research Foundation microbiologist Dr. Amy Proal pointed out that it might be impossible for the spike protein to remain in the body for long periods without the virus.

Other researchers have been pinning the long-term symptoms on a phenomenon called “viral persistence,” wherein the virus remains in the body even after the initial infection.

A previous study published in April reported that about 13% of former patients were still shedding viral RNA in their stools about four months after the infection. Additionally, nearly 4% continued to shed the same genetic material seven months later. The same people suffered gastrointestinal symptoms, including abdominal pain, nausea, and vomiting.

“The question is whether or not continued presence of the virus in the gut or elsewhere may kind of tickle the immune system, and cause there to be persistent symptoms,” Stanford University in California’s Ami Bhatt, who was involved in the April study, said.

Aside from the gut, researchers have also identified cases wherein the virus remained in the eyes, brain and heart. These organs serve as “anatomical sanctuaries” for the virus, so they can evade the immune system and continue to plague patients with long-term symptoms.

Unfortunately, more research is needed to really determine what is causing the long-term symptoms. For the many people living with the condition since the early days of the pandemic, the cure could only come about once long COVID is fully understood.