Introduction
The coronavirus disease-19 (COVID-19) is caused by a virus called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (Zhou, Yang et al. 2020). The virus is a single-stranded RNA virus coding for major structural surface glycoproteins: spike (S), matrix (M), envelope (E), and nucleoprotein (N) and a set of 16 nonstructural proteins (NSPs) as well as several additional open reading frames encoding for accessory proteins involved in host-virus interactions (Bartlam, Yang et al. 2005). The S protein is a homotrimeric protein consisting of the functional domains S1 and S2 which are responsible for binding of the virus to the angiotensin converting enzyme-2 (ACE2) (Shang, Ye et al. 2020). Spread of the virus is done by person to person contact via airborne droplets and aerosols. Most of the infected persons develop mildly symptomatic disease such as fever, cough, dyspnea, fatigue headache, dysgusia, anosmia, rhinorrhoea, vomiting and diarrhea, while 10 to 30% of infected persons remain asymptomatic (Marian 2021).
Antibody production has been documented in patients with acute infection within 21 days post infection onset, whereas persons with mild symptoms have low or undetectable levels of antibodies (Long, Liu et al. 2020, Long, Tang et al. 2020). T cell response has been investigated in COVID-19 patients after stimulation with N derived peptides using IFNγ-based enzyme-linked immunospots assays (IFNγ ELISPOT assays) demonstrating circulation of N-specific precursor cells in infected individuals. In contrast, low proportions of cells recognizing peptides derived from non-structural proteins (NSPs) were observed in those persons (Le Bert, Tan et al. 2020). Recently, preferential T helper cell type 1 (Th1) responses to S protein have been detected in patients with acute respiratory distress syndrome at early stages of the disease which increase over the time (Weiskopf, Schmitz et al. 2020).
The aim of this study was to evaluate the long-term humoral and cellular immune response to SARS-CoV-2-S-protein comparing individuals PCR-positive or –negative for SARS-CoV-2 from the first pandemic wave with Wuhan type SARS-CoV-2 in spring 2020 6 to 9 months after infection. This study identifies a set of persons diagnosed with positive SARS-CoV-2 PCR that did not develop positive serological or cellular immune responses to SARS-CoV-2 and underlines the importance to appeal to all reconvalescent individuals to get COVID-19 vaccination.