Sustained seroprevalence of anti SARS-CoV-2 total immunoglobulins in asymptomatic blood donors

Background: Seroprevalence analysis of SARS-CoV-2 is one of the keys to accurately monitor pandemics and help the authorities make health decisions and adjust the current social interventions. The aim of this study was to determine retrospective seroprevalence evolution among blood donors before pandemic, and along the first wave in Spain. A secondary objective was to determine whether age, blood group or haematological parameters are related to recent past infection. Material and Methods: A total of 12719 donations SARS-CoV-2 from July 2019 to October 2020 were analysed. Donors were 60.9% males and their average age was 46+/-13. An automated chemiluminiscence double-antigen sandwich immunoassay for the in vitro semi quantitative detection of total antibodies to SARS-CoV-2 in human serum and plasma was performed. Results: Seropositive donation rate grew up from week 11 to week 21, reaching plateau by near 8% donations, sustained until week 43 when 2nd wave arose in our country. 6.7% individuals were positive by the end of 1st wave. No differences by sex age or blood group were found regarding antibodies. Lymphocyte were significantly higher in positive woman as compared to negative ones and haemoglobin were lower in positive men as compared to negative ones. Discussion: Seroprevalence due to asymptomatic cases would be equivalent to that of general population. Sex and age would not affect COVID-19 susceptibility but its severity. Gender differences are present even in asymptomatic individuals: females are possibly protected by their relative lymphocytosis and neutropenia whereas males are would be weaker as seropositive men show a decrease of haematocrit and haemoglobin. Further studies are needed to confirm these gender differences not only in severe but as well in asymptomatic cases as they can help better understand COVID-19 pathogenesis and prognosis.