Dissecting the dynamics of SARS-CoV-2 reinfections in blood donors with pauci- or asymptomatic COVID-19 disease course at initial infection.

BACKGROUND: Understanding the dynamics of SARS-CoV-2 reinfections is crucial for public health policy, vaccine development, and long-term disease management. However, data on reinfections in the general population remains scarce. OBJECTIVES: This study aimed to investigate SARS-CoV-2 antibody dynamics among Austrian blood donors, representing healthy adults, over two years following primary infection and to evaluate the reinfection risk. METHODS: 117,895 blood donations were analysed for SARS-CoV-2 total anti-N levels from June 2020 to December 2023. We examined anti-N and anti-S antibody dynamics and in vitro functionality in 230 study participants at five defined times during 24 months, assessing associations with demographics, vaccination status, and reinfection awareness. RESULTS: The seroprevalence of SARS-CoV-2 infection-derived anti-N antibodies increased over time, reaching 90% by February 2023 and remaining at that level since then. According to serological screenings, we found an 88% reinfection rate, which is in contrast to participants' reports indicating a reinfection rate of 59%. Our data further reveal that about 26% of reinfections went completely unnoticed. Antibody dynamics were independent of age, sex, and ABO blood group. Interestingly, individuals with multiple reinfections reported symptoms more frequently during their primary infection. Our results further show that vaccination modestly affected reinfection risk and disease course. CONCLUSION: SARS-CoV-2 reinfections were uncommon until the end of 2021 but became common with the advent of Omicron. This study highlights the underestimation of reinfection rates in healthy adults and underscores the need for continued surveillance, which is an important support for public health policies and intervention strategies.

Epstein-Barr virus reactivation is not causative for post-COVID-19-syndrome in individuals with asymptomatic or mild SARS-CoV-2 disease course.

PURPOSE: Post-COVID-19-Syndrome (PCS) frequently occurs after an infection with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). However, the understanding of causative mechanisms is still limited. Aim of this study was to determine the PCS rate among SARS-CoV-2 seropositive blood donors as representatives of supposedly healthy adults, who had experienced an asymptomatic or mild COVID-19 disease course, and to examine whether Epstein-Barr virus (EBV) is reactivated in individuals reporting PCS. METHODS: The PCS rate was determined using questionnaires that included questions about infection and persistent symptoms. Pre-pandemic blood samples and samples collected at regular, pre-defined times after a SARS-CoV-2 infection were analysed for neopterin, a marker for antiviral immune responses, by an enzyme-linked immunosorbent assay (ELISA). Additionally, we determined the rate of SARS-CoV-2 anti-N total antibodies using an electrochemiluminescence immunoassay (ECLIA). Furthermore, quantitative real-time polymerase chain reaction (qPCR) to detect EBV DNA and ECLIA screening for EBV viral capsid-antigen (VCA) IgM, IgG and EBV nuclear antigen 1 (EBNA) IgG were performed. RESULTS: Our data reveal that 18% of all infections result in PCS, with symptoms lasting for up to one year. In individuals reporting PCS, no elevated levels of neopterin were detected, indicating no persisting pro-inflammatory, antiviral immune response. SARS-CoV-2 antibody levels were declining in all participants in comparable manner over time, pointing to a successful virus clearance. In individuals with PCS, no EBV DNA could be detected. Furthermore, no differences in EBV specific antibody levels could be shown in PCS groups compared to non-PCS groups. CONCLUSION: Our data suggest that PCS in per se healthy, immunocompetent adults cannot be ascribed to a reactivation of EBV.

Persistence of Naturally Acquired and Functional SARS-CoV-2 Antibodies in Blood Donors One Year after Infection.

The developmental course of antibodies produced after a SARS-CoV-2 infection has been insufficiently investigated so far. Therefore, the aim of this study was to investigate the dynamics of SARS-CoV-2 antibody levels against the viral nucleocapsid- and spike-protein among Austrian blood donors as a representative group of a supposedly healthy population within the first year after a SARS-CoV-2 infection. The impact of age, sex, vaccination status, AB0-blood group and awareness about the infection was evaluated. Our study shows that the level of anti-N antibodies is declining, while anti-S antibody levels remain stable. Antibodies detected were functional in vitro. Age, sex and blood group do not influence antibody dynamics. However, blood group AB shows significantly lower antibody levels and in vitro functionality compared to other blood groups. Our data reveal that one out of five individuals was not aware of a previous SARS-CoV-2 infection and that the disease course neither affects the level of antibody production nor the in vitro functionality. We also found that 14% of participants show persisting COVID-19-related symptoms for up to nine months. Our results provide valuable insights into the dynamics of the immune response after a SARS-CoV-2 infection in a representative cohort of adult blood donors in Central Europe.

Seroprevalence of anti-SARS-CoV-2 total antibody is higher in younger Austrian blood donors.

PURPOSE: Frequently the infection with coronavirus 2 (SARS-CoV-2) can be asymptomatic or provoke only mild symptoms. These cases often remain unnoticed, so it is difficult to estimate the actual numbers of infections. Aim of this study was to determine the seroprevalence of anti-SARS-CoV-2 total antibody in Austrian blood donors. METHODS: 20,228 blood donors aged between 18 and 72 years resident in four Austrian federal states were screened for anti-SARS-CoV-2 total antibody between 5th of June and 4th of December 2020. To evaluate the impact of sex, age, AB0-blood group and donation period on the anti-SARS-CoV-2 seroprevalence, multiple logistic regression was done. RESULTS: Our data reveal an anti-SARS-CoV-2 seroprevalence of 2.5% overall, significantly depending on the time point of blood donation: after the first Austrian lockdown the seroprevalence was lower compared to the following months, when the rate was constantly rising. While younger blood donors showed significantly higher seroprevalence, no differences were found concerning sex or AB0 blood group. CONCLUSION: Broad testing strategies are required to better determine the number of SARS-CoV-2 infections. Screening blood donors as a representative group for the adult population could be a valid tool to determine the number of recorded and unrecorded cases of SARS-CoV-2 infection.