SARS-CoV-2 is evolving with mutations in the receptor binding domain (RBD) being of particular concern. It is important to know how much cross-protection is offered between strains following vaccination or infection. Here, we obtain serum and saliva samples from groups of vaccinated (Pfizer BNT-162b2), infected and uninfected individuals and characterize the antibody response to RBD mutant strains. Vaccinated individuals have a robust humoral response after the second dose and have high IgG antibody titers in the saliva. Antibody responses however show considerable differences in binding to RBD mutants of emerging variants of concern and substantial reduction in RBD binding and neutralization is observed against a patient-isolated South African variant. Taken together our data reinforce the importance of the second dose of Pfizer BNT-162b2 to acquire high levels of neutralizing antibodies and high antibody titers in saliva suggest that vaccinated individuals may have reduced transmission potential. Substantially reduced neutralization for the South African variant further highlights the importance of surveillance strategies to detect new variants and targeting these in future vaccines.

The SARS-CoV-2 pandemic virus is consistently evolving with mutations within the receptor binding domain (RBD) being of particular concern. To date, there is little research into protection offered following vaccination or infection against RBD mutants in emerging variants of concern (UK, South African, Mink and Southern California). To investigate this, serum and saliva samples were obtained from groups of vaccinated (Pfizer BNT-162b2), infected and uninfected individuals. Antibody responses among groups, including salivary antibody response and antibody binding to RBD mutant strains were examined. The neutralization capacity of the antibody response against a patient-isolated South African variant was tested by viral neutralization tests and further verified by an ACE2 competition assay. We found that humoral responses in vaccinated individuals showed a robust response after the second dose. Interestingly, IgG antibodies were detected in large titers in the saliva of vaccinated subjects. Antibody responses showed considerable differences in binding to RBD mutants in emerging variants of concern. A substantial reduction in RBD binding and neutralization was detected for the South African variant. Taken together our data reinforces the importance of administering the second dose of Pfizer BNT-162b2 to acquire high levels of neutralizing antibodies. High antibody titers in saliva suggest that vaccinated individuals may have reduced transmission potential. Substantially reduced neutralization for the South African variant highlights importance of surveillance strategies to detect new variants and targeting these in future vaccines.

The pathophysiology of COVID-19 associated thrombosis seems to be multifactorial, involving interplay between cellular and plasmatic elements of the hemostasis. We hypothesized that COVID-19 is accompanied by platelet apoptosis with subsequent alteration of the coagulation system. We investigated depolarization of mitochondrial inner transmembrane potential (ΔΨm), cytosolic calcium (Ca2+) concentration, and phosphatidylserine (PS) externalization by flow cytometry. Platelets from intensive care unit (ICU) COVID-19 patients (n=21) showed higher ΔΨm depolarization, cytosolic Ca2+ concentration and PS externalization, compared to healthy controls (n=18) and COVID-19 non-ICU patients (n=4). Moreover significant higher cytosolic Ca2+ concentration and PS was observed compared to septic ICU control group (ICU control). In ICU control group (n=5; non-COVID-19 ICU) cytosolic Ca2+ concentration and PS externalization was comparable to healthy control, with an increase in ΔΨm depolarization. Sera from ICU COVID-19 patients induced significant increase in apoptosis markers (ΔΨm depolarization, cytosolic Ca2+ concentration and PS externalization) compared to healthy volunteer and septic ICU control. Interestingly, immunoglobulin G (IgG) fractions from COVID-19 patients induced an Fc gamma receptor IIA dependent platelet apoptosis (ΔΨm depolarization, cytosolic Ca2+ concentration and PS externalization). Enhanced PS externalization in platelets from ICU COVID-19 patients was associated with increased sequential organ failure assessment (SOFA) score (r=0.5635) and D-Dimer (r=0.4473). Most importantly, patients with thrombosis had significantly higher PS externalization compared to those without. The strong correlations between apoptosis markers and increased D-Dimer levels as well as the incidence of thrombosis may indicate that antibody-mediated platelet apoptosis potentially contributes to sustained increased thromboembolic risk in ICU COVID-19 patients.

Background Focused cardiac ultrasound (FCU) is a helpful tool to rapidly identify right ventricular (RV) causes of hemodynamic instability and facilitate the initiation of therapy. The clinical value of existing course models often remains unclear. This study investigated the effects of a one‐day FCU training on the visual estimation skills of RV characteristics. Methods Four residents were included as the study group after completing a standardized one‐day FCU training. Four gender‐matched controls did not take part in the training. All residents graded image quality, RV systolic function, and RV dimensions in a test comprising 35 ultrasound clips. Results The study and control group did not differ in ICU or ultrasound experience. Overall, training participants were able to distinguish between good and insufficient image quality significantly better than the control group (agreement 80.0% vs 61.4%, p = 0.04). The agreement for the estimation of RV function and RV dimensions was not different between the groups (63.2% vs 60.5%, p = 0.66 and 64.3% vs 67.1%, p = 0.18, respectively). Descriptively, only small differences were found between the groups for the estimation of RV function and RV dimensions in subgroups of patients with normal versus reduced systolic RV function or normal versus enlarged RV dimensions, respectively. Both groups struggled in identifying RV enlargement (34.6% vs 46.2%). Discussion In this study, a single one‐day FCU training had no impact on residents’ skills to visually assess systolic RV function or RV dimensions. Improvements of current training modalities or continuous teaching models are needed to optimize residency programs and patient care.