A study published in JCI Insight illustrated that coronavirus-specific immune responses are maintained in people with prolonged post-coronavirus symptom duration when compared to the people with resolved symptoms, thus indicating the persistence of viral antigens as an underlying etiology.

A subset of SARS-CoV-2 people demonstrates post-acute sequelae of COVID-19. But, there is little  awareness about the immune signatures linked with these syndromes. Researchers evaluated longitudinal peripheral blood samples in 50 people having prior confirmed coronavirus infection, including 20 who witnessed an extended duration of coronavirus symptoms (lasting for greater than 30 days; median = 74 days) in comparison with 30 who witnessed symptom resolution within 20 days.

The antigen-specific T cell response magnitudes to the circulating T follicular helper cell populations and coronavirus spike protein in CD4+ during the late convalescence were found to be maintained in people having extended duration of symptoms. On the other hand, people without persistent symptoms showed an expected decline. The prolonged group also illustrated raised IgG avidity to coronavirus spike protein. Substantial correlations were noted between symptom duration and both coronavirus-specific antibodies and  T cells.

The exhaustion and activation markers were determined in multiple immune cell types, showing few phenotypic differences between recovered and prolonged groups. This suggests that the extended duration of symptoms appears to be not due to persistent and sustained systemic inflammation.