Background: Early March 2020, a SARS-CoV-2 outbreak in the ski resort Ischgl in Austria initiated the spread of SARS-CoV-2 throughout Austria and Northern Europe. Methods: Between April 21 and 27, a cross-sectional epidemiologic study targeting the full population of Ischgl (n = 1867), of which 79 % could be included (n = 1473, incl. 214 children), was performed. For each individual, the study involved a SARS-CoV-2 PCR, antibody testing and structured questionnaires. A mathematical model was used to help understand the influence of the determined seroprevalence on virus transmission. Findings: The seroprevalence was 42.4% (95% CI 39.8–44.7). Individuals under 18 showed a significantly lower seroprevalence of 27.1% (95% CI 21.3–33.6) than adults (45%; 95% CI 42.2–47.7; OR of 0.455, 95% CI 0.356–0.682, p< 0.001). Of the seropositive individuals, 83.7% had not been diagnosed to have had SARS-CoV-2 infection previously. The clinical course was generally mild. Over the previous two months, two COVID-19-related deaths had been recorded, corresponding to an infection fatality rate (IFR) of 0.25% (95% CI 0.03–0.91). Only 8 (0.5 %) individuals were newly diagnosed to be infected with SARS-CoV-2 during this study. Interpretation: Ischgl was hit early and hard by SARS-CoV-2 leading to a high local seroprevalence of 42.4%, which was lower in individuals below the age of 18 than in adults. Mathematical modeling suggests that a drastic decline of newly infected individuals in Ischgl by the end of April occured due to the dual impact from the non-pharmacological interventions (NPIs) and a significant immunization of the Ischgl population. Funding: Helmholtz Association, European Union’s Horizon 2020 research and innovation program, German Research Foundation (DFG), state Tyrol.

In this study, we tested for antibody reactivities against gp120 and gp41-derived peptides, recombinant gp160, gp41 and tat in HIV-positive sera under antiretroviral therapy (ART) and determined their neutralization capacity. As a baseline, sera from patients in stage A, B and C of the disease, long term non-progressors (LNPs) and HIV-negative individuals were included. Compared to LNPs or sera from patients in group A, the reactivity of sera in stage B or C against gp120-derived peptides was reduced parallel to disease progression. Reactivity of these samples was compared with sera of patients under ART. Parallel to the decrease of viral load, the reactivity against gp120 and gp41-derived epitopes, recombinant gp160 and gp41 or the native gp120/41 complex was significantly reduced. Antibody-mediated neutralization of HIV-1 was detectable prior to ART but revealed substantial decreases coupled with progression of therapy. Responses to recombinant tat dropped after three months of therapy, increased however at later time points to initial levels. These data indicate that in parallel to the decrease in viral load and antibodies against gp120, the neutralization capacity of sera under ART is reduced, and can not be compensated by an increase in tat-specific antibodies.

We investigated the interplay between complement and antibodies upon priming with single-cycle replicating viral vectors (SCIV) encoding SIV antigens combined with Adeno5-SIV or SCIV pseudotyped with murine leukemia virus envelope boosting strategies. The vaccine was applied via spray-immunization to the tonsils of rhesus macaques and compared with systemic regimens. Independent of the application regimen or route, viral loads were significantly reduced after challenge with SIVmac239 (p < 0.03) compared to controls. Considerable amounts of neutralizing antibodies were induced in systemic immunized monkeys. Most of the sera harvested during peak viremia exhibited a trend with an inverse correlation between complement C3-deposition on viral particles and plasma viral load within the different vaccination groups. In contrast, the amount of the observed complement-mediated lysis did not correlate with the reduction of SIV titres. The heterologous prime-boost strategy with replication-deficient viral vectors administered exclusively via the tonsils did not induce any neutralizing antibodies before challenge. However, after challenge, comparable SIV-specific humoral immune responses were observed in all vaccinated animals. Immunization with single cycle immunodeficiency viruses mounts humoral immune responses comparable to live-attenuated immunodeficiency virus vaccines.