Monitoring the humoral protective immune response and its durability after SARS-CoV-2 infections is essential for risk assessment of reinfections, the improvement of diagnostic methods and the evaluation of vaccine trials. We have analyzed neutralizing antibodies and IgG responses specific to different antigens, including the inactivated whole-virion of SARS-CoV-2, the spike subunit 1 protein and its receptor binding domain, as well as the nucleocapsid protein. We show the dynamic developments of the responses from the early convalescent stages up to 9 months post symptoms onset in follow-up samples from 57 COVID-19 patients with varying clinical severity. By correlating antibody signals to neutralizing titres, valid diagnostic markers for the estimation of neutralizing protection could be identified.

Zika virus (ZIKV) is a zoonotic, human pathogenic, and mosquito-borne flavivirus. Its distribution is rapidly growing worldwide. Several attempts to develop vaccines for ZIKV are currently ongoing. Central to most vaccination approaches against flavivirus infections is the envelope (E) protein, which is the major target of neutralizing antibodies. Insect-cell derived, recombinantly expressed variants of E from the flaviviruses West Nile and Dengue virus have entered clinical trials in humans. Also for ZIKV, these antigens are promising vaccine candidates. Due to the structural similarity of flaviviruses, cross-reactive antibodies are induced by flavivirus antigens and have been linked to the phenomenon of antibody-dependent enhancement of infection (ADE). Especially the highly conserved fusion loop domain (FL) in the E protein is a target of such cross-reactive antibodies. In areas where different flaviviruses co-circulate and heterologous infections cannot be ruled out, this is of concern. To exclude the possibility that recombinant E proteins of ZIKV might induce ADE in infections with related flaviviruses, we performed an immunization study with an insect-cell derived E protein containing four mutations in and near the FL. Our data show that this mutant antigen elicits antibodies with equal neutralizing capacity as the wildtype equivalent. However, it induces much less serological cross-reactivity and does not cause ADE in vitro. These results indicate that mutated variants of the E protein might lead to ZIKV and other flavivirus vaccines with increased safety profiles.

Background: In 2015–2016, a large Zika virus (ZIKV) outbreak occurred in the Americas. Although the exact ZIKV antibody kinetics after infection are unknown, recent evidence indicates the rapid waning of ZIKV antibodies in humans. Therefore, we aimed to determine the levels of ZIKV antibodies more than three years after a ZIKV infection. Methods: We performed ZIKV virus neutralization tests (VNT) and a commercial ZIKV non-structural protein 1 (NS1) IgG ELISA in a cohort of 49 participants from Suriname who had a polymerase-chain-reaction-confirmed ZIKV infection more than three years ago. Furthermore, we determined the presence of antibodies against multiple dengue virus (DENV) antigens. Results: The ZIKV seroprevalence in this cohort, assessed with ZIKV VNT and ZIKV NS1 IgG ELISA, was 59.2% and 63.3%, respectively. There was, however, no correlation between these two tests. Furthermore, we did not find evidence of a potential negative influence of DENV immunity on ZIKV antibody titers. Conclusions: ZIKV seroprevalence, assessed with two commonly used serological tests, was lower than expected in this cohort of participants who had a confirmed previous ZIKV infection. This can have implications for future ZIKV seroprevalence studies and possibly for the duration of immunological protection after a ZIKV infection.

Immunization for the generation of protective antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has emerged to be highly effective in preventing hospital admission, need for intensive care treatment and high mortality in the current SARS-CoV-2 pandemic. Lateral flow immune assays (LFIAs) offer a simple and competitive option to monitor antibody production after vaccination. Here, we compared the diagnostic performance of three different lateral flow assays in detecting nucleocapsid protein (NP), S1 subunit (S1) and receptor binding domain (pseudo)-neutralizing antibodies (nRBD) in sera of 107 health care workers prior (V1), two weeks (V2) after first vaccination with BNT162b2 as well as three weeks (V3) and eight months later (V4). In sera at V1, overall specificity was >99%. At V3, LFIAs showed sensitivities between 98.1 and 100%. The comparison of S1 and nRBD LFIA with S1 ELISA and a focus reduction neutralization assay (FRNT) revealed high concordance at V3. Thus, the use of lateral flow immunoassays appears to have reasonable application in the short-term follow-up after vaccination for SARS-CoV-2.