Quantitative and Qualitative Difference in Antibody Response against Omicron and Ancestral SARS-CoV-2 after Third and Fourth Vaccination.

Waning immunity against SARS-CoV-2 and the emergence of variants, especially of the most distant variant, Omicron, affect titers of neutralizing antibodies in the sera of vaccinated individuals. Thus, two vaccinations with the mRNA vaccine BNT162b fail to induce neutralizing antibodies against the Omicron variant. A first booster vaccination increases Omicron-RBD-binding IgG and IgA and neutralizing capacity. In comparison, the Wuhan isolate titers of the Omicron variant binding antibodies are 8.5 lower. After a third vaccination, induction of Omicron-RBD- and Wuhan-RBD-binding antibodies follows the same kinetic. Five to six months after the third vaccination, there are still Omicron-RBD-binding antibodies detectable, but 35.9 percent of the analyzed sera fail to neutralize the Omicron variant, while all sera efficiently neutralize the Delta isolate. In the case of the Wuhan-RBD, a significantly larger number of stable antigen-antibody complexes is formed than in Omicron-RBD. A fourth vaccination with mRNA-1273 temporarily restores levels of Omicron-, Delta- and Wuhan-specific antibodies. Comparing different booster strategies revealed that the breadth of the immune response is not affected by the vaccination regimen. Taken together, these data indicate that booster vaccinations (third and fourth dose) increase the breadth of the immune response, but there is a qualitative difference of antibodies with respect to the stability of antigen-antibody complexes and persistence of antibody titers.

The SARS-CoV-2 Variant Omicron Is Able to Escape Vaccine-Induced Humoral Immune Responses, but Is Counteracted by Booster Vaccination.

The SARS-CoV-2 variant Omicron has spread world-wide and is responsible for rapid increases in infections, including in populations with high vaccination rates. Here, we analysed in the sera of vaccinated individuals the antibody binding to the receptor-binding domain (RBD) of the spike protein and the neutralization of wild-type (WT), Delta (B.1.617.2), and Omicron (B.1.1.529; BA.1) pseudotyped vectors. Although sera from individuals immunized with vector vaccines (Vaxzevria; AZ and COVID-19 Janssen, Ad26.COV2.S; J&J) were able to bind and neutralize WT and Delta, they showed only background levels towards Omicron. In contrast, mRNA (Comirnaty; BNT) or heterologous (AZ/BNT) vaccines induced weak, but detectable responses against Omicron. While RBD-binding antibody levels decreased significantly six months after full vaccination, the SARS-CoV-2 RBD-directed avidity remained constant. However, this still coincided with a significant decrease in neutralization activity against all variants. A third booster vaccination with BNT significantly increased the humoral immune responses against all tested variants, including Omicron. In conclusion, only vaccination schedules that included at least one dose of mRNA vaccine and especially an mRNA booster vaccination induced sufficient antibody levels with neutralization capacity against multiple variants, including Omicron.

Long-term outcome of patients with vaccine-induced immune thrombotic thrombocytopenia and cerebral venous sinus thrombosis.

We present the long-term outcomes of 44 patients who developed cerebral venous sinus thrombosis after vaccination with the adenoviral vector ChAdOx1 nCoV-19 COVID-19 vaccine. Assessment of the Extended Glasgow Outcome Scale was performed within 3-6 months after the initial hospital admissions. Patient outcomes ranged from good recovery (13 patients, 29.6%) to moderate disability (11 patients, 25.0%) and severe disability or vegetative state (6 patients, 13.6%). Fatal outcomes were reported in 14 patients (31.8%).

Analysis of BNT162b2- and CVnCoV-elicited sera and of convalescent sera toward SARS-CoV-2 viruses.

BACKGROUND: The mRNA vaccine BNT162b2 (Comirnaty, BioNTech/Pfizer) and the vaccine candidate CVnCoV (Curevac) each encode a stabilized spike protein of SARS-CoV2 as antigen but differ with respect to the nature of the mRNA (modified versus unmodified nucleotides) and the mRNA amount (30 µg versus 12 µg RNA). This study characterizes antisera elicited by these two vaccines in comparison to convalescent sera. METHODS: Sera from BNT162b2 vaccinated healthcare workers, and sera from participants of a phase I trial vaccinated with 2, 4, 6, 8, or 12 µg CVnCoV and convalescent sera from hospitalized patients were analyzed by ELISA, neutralization tests, surface plasmon resonance (SPR), and peptide arrays. RESULTS: BNT162b2-elicited sera and convalescent sera have a higher titer of spike-RBD-specific antibodies and neutralizing antibodies as compared to the CVnCoV-elicited sera. For all analyzed sera a reduction in binding and neutralizing antibodies was found for the lineage B.1.351 variant of concern. SPR analyses revealed that the CVnCoV-elicited sera have a lower fraction of slow-dissociating antibodies. Accordingly, the CVnCoV sera almost fail to compete with the spike-ACE2 interaction. The significance of common VOC mutations K417N, E484K, or N501Y focused on linear epitopes was analyzed using a peptide array approach. The peptide arrays showed a strong difference between convalescent sera and vaccine-elicited sera. Specifically, the linear epitope at position N501 was affected by the mutation and elucidates the escape of viral variants to antibodies against this linear epitope. CONCLUSION: These data reveal differences in titer, neutralizing capacity, and affinity of the antibodies between BNT162b2- and CVnCoV-elicited sera, which could contribute to the apparent differences in vaccine efficacy.

Comirnaty-Elicited and Convalescent Sera Recognize Different Spike Epitopes.

Many of the approved SARS-CoV-2 vaccines are based on a stabilized variant of the spike protein. This raises the question of whether the immune response against the stabilized spike is identical to the immune response that is elicited by the native spike in the case of a SARS-CoV-2 infection. Using a peptide array-based approach, we analysed the binding of antibodies from Comirnaty-elicited, convalescent, and control sera to the peptides covering the spike protein. A total of 37 linear epitopes were identified. A total of 26 of these epitopes were almost exclusively recognized by the convalescent sera. Mapping these epitopes to the spike structures revealed that most of these 26 epitopes are masked in the pre-fusion structure. In particular, in the conserved central helix, three epitopes that are only exposed in the post-fusion conformation were identified. This indicates a higher spike-specific antibody diversity in convalescent sera. These differences could be relevant for the breadth of spike-specific immune response.

Persistence of infectious SARS-CoV-2 particles for up to 37 days in patients with mild COVID-19.

BACKGROUND: People suffering from COVID-19 are typically considered non-infectious 14 days after diagnosis if symptoms have disappeared for at least 48 h. We describe three patients who independently acquired their infection. These three patients experienced mild COVID-19 and completely recovered symptomatically within 10 days, but remained PCR-positive in deep pharyngeal samples for at least 38 days. We attempted to isolate virus from pharyngeal swabs to investigate whether these patients still carried infectious virus. METHODS: Infectious virus was amplified in Vero E6 cells and characterized by electron microscopy and WGS. The immune response was investigated by ELISA and peptide arrays. RESULTS: In all three cases, infectious and replication-competent virus was isolated and amplified in Vero E6 cells. Virus replication was detected by RT-PCR and immunofluorescence microscopy. Electron microscopy confirmed the formation of intact SARS-CoV-2 particles. For a more detailed analysis, all three isolates were characterized by whole-genome sequencing (WGS). The sequence data revealed that the isolates belonged to the 20A or 20C clade, and two mutations in ORF8 were identified among other mutations that could be relevant for establishing a long-term infection. Characterization of the humoral immune response in comparison to patients that had fully recovered from mild COVID-19 revealed a lack of antibodies binding to sequential epitopes of the receptor-binding domain (RBD) for the long-term infected patients. CONCLUSION: Thus, a small portion of COVID-19 patients displays long-term infectivity and termination of quarantine periods after 14 days, without PCR-based testing, should be reconsidered critically.

SARS-CoV-2 asymptomatic and symptomatic patients and risk for transfusion transmission.

Oral swabs, sputum, and blood samples from 18 asymptomatic and symptomatic patients with SARS-CoV-2 infection were examined using RT-PCR testing in order to assess the risk of transfusion-related transmission. In asymptomatic patients as well as patients with flu-like symptoms and fever, no SARS-CoV-2 RNA could be detected in the blood or serum despite a clearly positive result in all throat swabs. As patients with symptoms of infectious disease will not be admitted to blood donation, the risk for transfusion transmission of SARS-CoV-2 seems to be negligible.