Scientists haven’t figured out long Covid. Here are 5 of their best hypotheses. - Vox.com

But the latest research suggests that at least 10 percent have long-term symptoms, even after their body has apparently cleared the virus.

It’s also possible the coronavirus causes long-term symptoms even more frequently than other infections.

The first explanation for what might cause persistent symptoms in people who’ve been infected with Covid-19 is the simplest: The virus or its components might still be lurking in the body somewhere, long after a person starts testing negative.

A related explanation for what might be happening with long-Covid patients is what Iwasaki calls “viral ghosts.” While the intact virus may have left the body, “there may be RNA and protein from the virus that’s lingering and continuing to stimulate the immune system,” Iwasaki said.

“It’s almost like having a chronic viral infection — it keeps stimulating the immune system because the virus or viral components are still there, and the body doesn’t know how to shut it off.”.

Other pathogens already lurking in the body prior to a coronavirus infection might also exacerbate symptoms.

The virus interrupts normal immune function, causing it to misfire, so that molecules that normally target foreign invaders — like viruses — turn on the body.

In one study, researchers tracked blood and stool samples from 100 patients hospitalized with SARS-CoV-2 infection, testing some up to 30 days after they cleared the virus.

(They also collected samples from a control group for comparison.) And they found Covid-19 infection was linked to a “dysbiotic gut microbiome,” even after the virus cleared the respiratory tract; they also hypothesized that it might contribute to the persistent health problems some patients are experiencing.

The virus might have cleared the body but left injuries in its wake — scars in the lungs or damage to the heart, for example — and these injuries might give rise to symptoms.

According to a recent preprint involving 201 patients, 70 percent had impairments in one or more organs four months after their initial Covid-19 symptoms set in.