Studies find distinct biomarkers and health impacts of long COVID, though some experts urge caution on overestimating prevalence

Multiple studies show clear biological differences in long COVID patients, including irregular immune responses and lower cortisol levels.
CDC survey estimates around 18 million U.S. adults have experienced long COVID symptoms.
Some experts argue flawed research methodologies may be leading to overestimation of long COVID prevalence.
Well-designed studies with control groups are needed to precisely determine long COVID's impacts.
Researchers hope discoveries may lead to diagnostic testing and tailored treatments for long COVID sufferers.