The new WHO reference standard allows for the definition of serum antibodies against various SARS-CoV-2 antigens in terms of binding antibody units (BAU/mL) and thus to compare the results of ...different ELISA systems. In this study, the concentration of antibodies (ABs) against both the S- and the N-protein of SARS-CoV-2 as well as serum neutralization activity were evaluated in three patients after a mild course of COVID-19. Serum samples were collected frequently during a period of over one year. Furthermore, in two individuals, the effects of an additional vaccination with a mRNA vaccine containing the S1-RBD sequence on these antibodies were examined. After natural infection, the antibodies (IgA, IgG) against the S1-protein remained elevated above the established cut-off to positivity (S-IgA 60 BAU/mL and S-IgG 50 BAU/mL, respectively) for over a year in all patients, while this was not the case for ABs against the N-protein (cut-off N-IgG 40 BAU/mL, N-IgA 256 BAU/mL). Sera from all patients retained the ability to neutralize SARS-CoV-2 for more than a year. Vaccination resulted in a rapid boost of antibodies to S1-protein but, as expected, not to the N-protein. Most likely, the wide use of the WHO reference preparation will be very useful in determining the individual immune status of patients after an infection with SARS-CoV-2 or after vaccination.
The relationship between the nasopharyngeal virus load, IgA and IgG antibodies to both the S1-RBD-protein and the N-protein, as well as the neutralizing activity (NAbs) against SARS-CoV-2 in the ...blood of moderately afflicted COVID-19 patients, needs further longitudinal investigation. Several new serological methods to examine these parameters were developed, validated and applied in three patients of a family which underwent an ambulatory course of COVID-19 for six months. The virus load had almost completely disappeared after about four weeks. Serum IgA levels to the S1-RBD-protein and, to a lesser extent, to the N-protein, peaked about three weeks after clinical disease onset but declined soon thereafter. IgG levels rose continuously, reaching a plateau at approximately six weeks, and stayed elevated over the observation period. Virus-neutralizing activity reached a peak about 4 weeks after disease onset but dropped slowly. The longitudinal associations of virus neutralization and the serological immune response suggest immunity in patients even after a mild clinical course of COVID-19.
Hepatitis A virus (HAV) strain HAV/HFS/GBM was adapted to and grown in human diploid fibroblast cells. The HAV was concentrated by ammonium sulphate precipitation and high-speed centrifugation. The ...virus was inactivated by beta-propiolacton and purified by sedimentation through a 20% solution of sucrose and by CsCl gradient centrifugation. The immunogenicity of different preparations was tested in mice, guinea pigs, and goats. The immune response after vaccination was tested by determination of anti-HAV with RIA and of neutralizing antibodies with an appropriate test system. Results showed that anti-HAV titers of 1:1,000 and greater, as well as neutralizing antibody titers of 1:1,000 and greater, were found in sera of animals vaccinated with different preparations. It became evident that good anti-HAV titers persisted over a period of at least 1.5 years in goats and mice after immunization with a semipurified HAV vaccine, and titers up to 1:200 were present in mice 2 years after vaccination with a highly purified HAV vaccine.
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