Class switch towards non-inflammatory IgG isotypes after repeated SARS-CoV-2 mRNA vaccination (preprint)

Repeated mRNA vaccinations are an efficient tool to combat the SARS-CoV-2 pandemic. High levels of neutralizing SARS-CoV-2-antibodies are an important component of vaccine-induced immunity. Shortly after the first or second mRNA vaccine dose, the IgG response mainly consists of the pro-inflammatory isotypes IgG1 and IgG3 and is driven by T helper (Th) 1 cells. Here, we report that several months after the second vaccination, SARS-CoV-2-specific antibodies were increasingly composed of non-inflammatory IgG2 and particularly IgG4, which were further boosted by a third mRNA vaccination and/or SARS-CoV-2 variant breakthrough infections. While IgG antibodies were affinity matured and of high neutralization capacity, the switch in constant domains caused changes in fragment crystallizable (Fc)-receptor mediated effector functions, including a decreased capacity to facilitate phagocytosis. IgG4 induction was neither induced by Th2 cells nor observed after homologous or heterologous SARS-CoV-2 vaccination with adenoviral vectors. In addition, IgG2- and IgG4-producing memory B cells were phenotypically indistinguishable from IgG1- or IgG3-producing cells. Since Fc-mediated effector functions are critical for antiviral immunity, the described class switch towards non-inflammatory IgG isotypes, which otherwise rarely occurs after vaccination or viral infection, may have consequences for the choice and timing of vaccination regimens using mRNA vaccines.

Dynamics of humoral and cellular immune responses after homologous and heterologous SARS-CoV-2 vaccination with ChAdOx1 nCoV-19 and BNT162b2 (preprint)

Vaccines are the most important means to overcome the SARS-CoV-2 pandemic. They induce specific antibody and T-cell responses but it remains open how well vaccine-induced immunity is preserved over time following homologous and heterologous immunization regimens. Here, we compared the dynamics of humoral and cellular immune responses up to 5 months after homologous or heterologous vaccination with either ChAdOx1-nCoV-19 (ChAd) or BNT162b2 (BNT) or both. Antibody responses significantly waned after vaccination, irrespective of the regimen. The capacity to neutralize SARS-CoV-2 - including variants of concern such as Delta or Omicron - was superior after heterologous compared to homologous BNT vaccination, both of which resulted in longer-lasting humoral immunity than homologous ChAd immunization. T-cell responses showed less waning irrespective of the vaccination regimen. These findings demonstrate that heterologous vaccination with ChAd and BNT is a potent approach to induce long-term humoral and cellular immune protection.

Superior immunity that allows neutralization of all SARS-CoV-2 variants of concern develops in COVID-19 convalescents and naïve individuals after three vaccinations (preprint)

Infection-neutralizing antibody responses after SARS-CoV-2 infection or COVID-19 vaccination are an essential part of antiviral immunity. This immune protection is challenged by the occurrence of SARS-CoV-2 variants of concern (VoCs) with immune escape properties, such as omicron (B.1.1.529) that is rapidly spreading worldwide. Here, we report neutralizing antibody dynamics in a longitudinal cohort of COVID-19 convalescent and naïve individuals vaccinated with mRNA BNT162b2 by quantifying anti-SARS-CoV-2-spike antibodies and determining their avidity and neutralization capacity. A superior infection-neutralizing capacity against all VoCs, including omicron, developed by either two vaccinations of convalescents, or a third vaccination or breakthrough infection of twice-vaccinated naïve individuals. These three consecutive spike antigen exposures resulted in an increasing neutralization capacity per anti-spike antibody unit and were paralleled by stepwise increases in antibody avidity. In conclusion, an infection/vaccination-induced hybrid immunity or a triple immunization induces high-quality antibodies resulting in superior neutralization capacity against VoCs, including omicron.

Active Surveillance of Adverse Events After COVID-19 and Other Vaccinations: a Feasibility Study as Part of the CoVaKo Project (preprint)

Background: The Corona-Vakzin-Konsortium project (CoVaKo) analyses the efficacy and safety of COVID-19 vaccines in a real-world setting and breakthrough infections in Bavaria, Germany. A subproject of CoVaKo aims to identify adverse events of the COVID-19 vaccine and to compare these to adverse events of other vaccines in an online survey. A prior feasibility study was conducted to test study materials for comprehensibility, visual design and motivation to participate and secondly, to test practical implementation and realization in primary care practices and vaccination centres. Methods: : A mixed-methods design was used. Three focus groups with general population participants were performed to evaluate the study materials and survey. Second, a test-roll-out was conducted in vaccination centres and primary care practices, which involved implementation and quantitative evaluation of the online survey. Third, interviews were conducted with participating general practitioners and heads of vaccination centres four weeks after the test-roll-out. Results: : Parts of the study information and registration form proved incomprehensible in the recruitment material and/or online survey. For example, headings were misleading since the COVID-19 vaccination was overemphasized in the title as compared to other vaccinations. Participants requested more information on the procedure and completion time. In 31 days, 2199 participants who received either a COVID-19 vaccination (99 %) or at least one of the control vaccinations (1 %) registered for the study. Participants (strongly) agreed that the registration process was easy to understand, that all relevant information was provided, the completion time was reasonable and technical framework manageable. Physicians and heads of the vaccination centres perceived the study as easy to integrate into their workflow and most of them were willing to participate in the main study. Conclusions: : Our study indicated that capturing adverse events after vaccinations with an online survey is feasible. Testing of materials and surveys provided valuable improvements. Participation of health professionals is important to ensure practicality of the procedures. Flexible adaptation of the study organization to changing structures and requirements is necessary for a successful implementation, especially due to dynamic changes in COVID-19 vaccination strategies. Trial registration: The trial was retrospectively registered at “Deutsches Register Klinischer Studien” (DRKS-ID: DRKS00025881) on Oct 14, 2021.

Heterologous prime-boost vaccination with ChAdOx1 nCoV-19 and BNT162b2 mRNA (preprint)

Administration of a first dose of the COVID-19 vaccine ChAdOx1 nCoV-19 (Vaxzevria(R), AstraZeneca) is associated with a certain risk for vaccine-induced immune thrombotic thrombocytopenia. Therefore, several countries have recommended replacing the second dose of ChAdOx1 nCoV-19 with an mRNA-based vaccine as a precautionary measure, although data on safety and efficacy of such heterologous prime-boost regimen are sparse. Therefore, vaccinees, who had received a heterologous vaccination using ChAdOx1 nCoV-19 as prime and BNT162b2 (Comirnaty(R), BioNTech-Pfizer) mRNA as boost vaccination were offered SARS-CoV-2 antibody testing to quantify their vaccine-induced neutralizing antibody response. The results were compared to cohorts of healthcare workers or volunteers, who received homologous BNT162b2 or homologous ChAdOx1 nCoV-19 vaccination regimens, respectively. A striking increase of vaccine-induced SARS-CoV-2 neutralizing antibody activity was observed in 229 vaccinees that received a BNT162b2 boost 9 to 12 weeks after ChAdOx1 nCoV-19 prime. In our cohort comprising over 480 individuals, the heterologous vaccination scheme induced significantly higher neutralizing antibody titers than homologous ChAdOx1 nCoV-19 and even than homologous BNT162b2 vaccination. This proves that a single dose of a COVID-19 mRNA vaccine after ChAdOx1 nCoV-19 prime vaccination is sufficient to achieve high neutralizing antibody levels predicting immune protection from SARS-CoV-2 infection, and may even increase vaccine efficacy offering an alternative in a setting of vaccine shortage.

Estimates and determinants of SARS-CoV-2 seroprevalence and infection fatality ratio using latent class analysis: the population-based Tirschenreuth study in the hardest-hit German county in spring 2020 (preprint)

SARS-CoV-2 infection fatality ratios (IFR) remain controversially discussed with implications for political measures, but the number of registered infections depends on testing strategies and deduced case fatality ratios (CFR) are poor proxies for IFR. The German county of Tirschenreuth suffered a severe SARS-CoV-2 outbreak in spring 2020 with particularly high CFR. To estimate seroprevalence, dark figure, and IFR for the Tirschenreuth population aged [≥]14 years in June/July 2020 with misclassification error control, we conducted a population-based study, including home visits for elderly, and analyzed 4203 participants for SARS-CoV-2 antibodies via three antibody tests (64% of our random sample). Latent class analysis yielded 8.6% standardized county-wide seroprevalence, dark figure factor 5.0, and 2.5% overall IFR. Seroprevalence was two-fold higher among medical workers and one third among current smokers with similar proportions of registered infections. While seroprevalence did not show an age-trend, the dark figure was 12.2 in the young versus 1.7 for [≥]85-year-old. Age-specific IFRs were <0.5% below 60 years of age, 1.0% for age 60-69, 13.2% for age 70+, confirming a previously reported age-model for IFR. Senior care homes accounted for 45% of COVID-19-related deaths, reflected by an IFR of 7.5% among individuals aged 70+ and an overall IFR of 1.4% when excluding senior care home residents from our computation. Our data underscore senior care home infections as key determinant of IFR additionally to age, insufficient targeted testing in the young, and the need for further investigations on behavioral or molecular causes of the fewer infections among current smokers.

Rapid response flow cytometric assay for the detection of antibody responses to SARS-CoV-2 (preprint)

SARS-CoV-2 has emerged as a previously unknown zoonotic coronavirus that spread worldwide causing a serious pandemic. While reliable nucleic acid-based diagnostic assays were rapidly available, there exists only a limited number of validated serological assays. Here, we evaluated a novel flow cytometric approach based on antigen-expressing HEK 293T cells to assess spike-specific IgG and IgM antibody responses. Analyses of 201 pre-COVID-19 sera proved a high assay specificity in comparison to commercially available CLIA and ELISA systems, while also revealing the highest sensitivity in specimens from PCR-confirmed SARS-CoV-2 infected patients. Additionally, a soluble Angiotensin-Converting-Enzyme 2 (ACE-2) variant was established as external standard to quantify spike-specific antibody responses on different assay platforms. In conclusion, our newly established flow cytometric assay allows sensitive and quantitative detection of SARS-CoV-2-specific antibodies, which can be easily adopted in different laboratories and does not rely on external supply of assay kits.