There have been many studies examining why some people experience “long covid” and others do not, but the diagnosis and treatment of post-acute sequelae of COVID-19 (PASC) continues to challenge health care providers.
A study, published in medRxiv, attempted to identify PASC biomarkers to improve the long-term diagnosis of COVID. The team of researchers, from Brigham and Women’s Hospital and Massachusetts General Hospital, found that excess SARS-CoV-2 spike protein in plasma indicated long COVID.
The researchers analyzed plasma samples collected from 63 individuals previously infected with COVID-19, 37 of whom were diagnosed with PASC. Blood samples were collected at least 2 times and no more than 12 months after an RT-PCR or COVID-19 positive antibody test. As a control, blood samples were also collected from 26 people who contracted COVID-19 but who recovered completely, without any diagnosis of PASC.
The researchers used matrix assays of ultrasensitive individual molecules to measure the concentration of COVID-19 antigens. They detected the S1 subunit of spike, full-length spike, or nucleocapsid (N) in 65% of the plasma of patients with PASC. Of the 3 measured antigens, the peak was detected most frequently, in 60% of patients. In particular, no peak could be detected in patients with fully recovered COVID-19.
Of the 37 long-term patients with COVID, 30 were women, which confirmed the results of previous research that women are disproportionately affected by PASC. Of the 26 undiagnosed patients with PASC, 10 were admitted to the intensive care unit (ICU) and 7 were intubated.
The presence of SARS-CoV-2 spike antigen in most patients with PASC suggests that long COVID may be due to the active presence of a SARS-CoV-2 viral reservoir. The researchers noted that their sample size was small, but it is significant that a peak was detected at various times between 2 and 12 months after COVID-19 infection.