New research indicates that people with this condition have a dysregulated complement system. The discovery opens the door to drug development and diagnostic tests

Four years are about to pass since the outbreak of a pandemic that shook the world and although the Covid virus is now under control, its hangover still weighs on millions of people. Long Covid — which is associated with more than 200 symptoms — affects one in eight people. Scientists are still trying to decipher what is behind this heterogeneous disease. Some studies point to immune dysfunction; others to viral reservoirs hiding in the body. Researchers also believe it is connected to persistent inflammation; but the fundamental mechanism remains unclear.

A study published on Thursday in the prestigious journal Science sheds light on the disease by identifying a potential biomarker in blood to detect long Covid. Researchers found that people with long Covid exhibited changes to blood serum proteins in the complement system, a network of molecules that participates in the destruction of pathogens. The finding highlights the key role the immune system plays in the development of long Covid and opens the door to drugs aimed at reversing this dysfunction in the body’s lines of defense.

By January 2020, the Sars-Cov-2 virus was already spreading silently around the globe and the first cases of Covid were beginning to break out everywhere. Four years later, around 778 million people have been infected, and seven million have died, according to the World Health Organization. But the thousands of people with long Covid are not included in the statistics. While they do not have an active infection, they suffer from symptoms such as fatigue, brain fog, muscle pain, breathing problems — sometimes all at once.