While the true number of long Covid sufferers is difficult to determine, the WHO says it could be between 10-20% of all people who have contracted the disease.
One notable study released last month showed there were significant differences in the proteins of the blood of more than 110 long-Covid patients. Onur Boyman, a Swiss researcher and senior author of the Science study, said he believes this is a “central puzzle piece” in what keeps Covid raging for so long in the bodies of some people.
Part of the body’s immune system called the complement system, which normally fights off infection by killing infected cells, remains active in people with long Covid, continuing to attack healthy targets and causing tissue damage, the researchers said. Boyman said that when people recovered from long Covid, their complement system also improved, suggesting a strong link between the two. “It shows that long Covid is a disease and you can actually measure it,” Boyman said.
Researchers not involved in the study cautioned that this complement system “dysregulation” could not explain all the different ways that long Covid seems to attack patients.
Ziyad Al-Aly, an epidemiologist at Washington University, St Louis, said long Covid has been so elusive because it is a “multi-system disease”. “Our minds are trained to think of diseases based on organ systems” such as heart or lung disease, he said.