Prioritising older individuals for COVID-19 booster vaccination leads to optimal public health outcomes in a range of socio-economic settings.

The rapid development of vaccines against SARS-CoV-2 altered the course of the COVID-19 pandemic. In most countries, vaccinations were initially targeted at high-risk populations, including older individuals and healthcare workers. Now, despite substantial infection- and vaccine-induced immunity in host populations worldwide, waning immunity and the emergence of novel variants continue to cause significant waves of infection and disease. Policy makers must determine how to deploy booster vaccinations, particularly when constraints in vaccine supply, delivery and cost mean that booster vaccines cannot be administered to everyone. A key question is therefore whether older individuals should again be prioritised for vaccination, or whether alternative strategies (e.g. offering booster vaccines to the individuals who have most contacts with others and therefore drive infection) can instead offer indirect protection to older individuals. Here, we use mathematical modelling to address this question, considering SARS-CoV-2 transmission in a range of countries with different socio-economic backgrounds. We show that the population structures of different countries can have a pronounced effect on the impact of booster vaccination, even when identical booster vaccination targeting strategies are adopted. However, under the assumed transmission model, prioritising older individuals for booster vaccination consistently leads to the most favourable public health outcomes in every setting considered. This remains true for a range of assumptions about booster vaccine supply and timing, and for different assumed policy objectives of booster vaccination.

Use of Adjuvant Compositions Based on Squalene Ensures Induction of Neutralizing Antibodies against SARS-CoV-2.

Squalene-based adjuvant compositions that can provide effective induction of specific humoral immune response have been developed. Recombinant receptor-binding domain (RBD) of surface S-protein of SARS-CoV-2 was used to evaluate the properties of the composition. Immunization of mice with the developed squalene-based compositions in combination with RBD allows obtaining high titers of specific antibodies: from 105 to 2×106. The blood sera from immunized mice exhibit neutralizing activity against SARS-CoV-2 Delta variant (B.1.617.2) with a titer up to 1:2000.

Multiple vaccine comparison in the same adults reveals vaccine-specific and age-related humoral response patterns: an open phase IV trial.

Vaccine responsiveness is often reduced in older adults. Yet, our lack of understanding of low vaccine responsiveness hampers the development of effective vaccination strategies to reduce the impact of infectious diseases in the ageing population. Young-adult (25-49 y), middle-aged (50-64 y) and older-adult ( ≥ 65 y) participants of the VITAL clinical trials (n = 315, age-range: 28-98 y), were vaccinated with an annual (2019-2020) quadrivalent influenza (QIV) booster vaccine, followed by a primary 13-valent pneumococcal-conjugate (PCV13) vaccine (summer/autumn 2020) and a primary series of two SARS-CoV-2 mRNA-1273 vaccines (spring 2021). This unique setup allowed investigation of humoral responsiveness towards multiple vaccines within the same individuals over the adult age-range. Booster QIV vaccination induced comparable H3N2 hemagglutination inhibition (HI) titers in all age groups, whereas primary PCV13 and mRNA-1273 vaccination induced lower antibody concentrations in older as compared to younger adults (primary endpoint). The persistence of humoral responses, towards the 6 months timepoint, was shorter in older adults for all vaccines (secondary endpoint). Interestingly, highly variable vaccine responder profiles overarching multiple vaccines were observed. Yet, approximately 10% of participants, mainly comprising of older male adults, were classified as low responders to multiple vaccines. This study aids the identification of risk groups for low vaccine responsiveness and hence supports targeted vaccination strategies. Trial number: NL69701.041.19, EudraCT: 2019-000836-24.

Impact of COVID-19 on vaccine confidence and uptake: A systematic literature review.

During the coronavirus disease 2019 (COVID-19) pandemic, scheduled vaccinations were postponed, mass vaccination programmes were suspended and opportunities for healthcare workers to administer vaccines ad hoc decreased. The aims of this systematic literature review were to determine the impact of the COVID-19 pandemic on vaccine confidence, intent and uptake in preexisting routine childhood or adult vaccination programmes, and to identify factors associated with changes in acceptance, intent and uptake of preexisting vaccines. Medline and Embase were searched for studies in Australia, Brazil, Canada, China, Japan, the USA, and European countries, published between 1 January 2021 and 4 August 2022. A complementary gray literature search was conducted between 11 and 13 October 2022, and supplemented with additional gray research in October 2023. In total, 54 citations were included in the review. Study design and geography were heterogeneous. The number of adults who received or intended to receive an influenza or pneumococcal vaccine was higher during the pandemic than in previous seasons (n = 28 studies). In addition, increased acceptance of adult vaccinations was observed during 2020-21 compared with 2019-20 (n = 12 studies). The rates of childhood vaccinations decreased during the COVID-19 pandemic across several countries (n = 11 studies). Factors associated with changes in intention to receive a vaccination, or uptake of influenza vaccine, included previous vaccination, older age, higher perceived risk of contracting COVID-19, anxiety regarding the pandemic and fear of contracting COVID-19. Acceptance and uptake of influenza and pneumococcal vaccines generally increased after onset of the COVID-19 pandemic.

Efficacy, immunogenicity and safety of CoronaVac® in children and adolescents aged 6 months to 17 years: a multicenter, randomized, double-blind, placebo-controlled phase III clinical trial.

Safe and effective vaccines against COVID-19 for children and adolescents are needed. This international multicenter, randomized, double-blind, placebo-controlled, phase III clinical trial assessed the efficacy, immunogenicity, and safety of CoronaVac® in children and adolescents (NCT04992260). The study was carried out in Chile, South Africa, Malaysia, and the Philippines. The enrollment ran from September 10, 2021 to March 25, 2022. For efficacy assessment, the median follow-up duration from 14 days after the second dose was 169 days. A total of 11,349 subjects were enrolled. Two 3-µg injections of CoronaVac® or placebo were given 28 days apart. The primary endpoint was the efficacy of the CoronaVac®. The secondary endpoints were the immunogenicity and safety. The vaccine efficacy was 21.02% (95% CI: 1.65, 36.67). The level of neutralizing antibody in the vaccine group was significantly higher than that in the placebo group (GMT: 390.80 vs. 62.20, P <0.0001). Most adverse reactions were mild or moderate. All the severe adverse events were determined to be unrelated to the investigational products. In conclusion, in the Omicron-dominate period, a two-dose schedule of 3 µg CoronaVac® was found to be safe and immunogenic, and showed potential against symptomatic COVID-19 in healthy children and adolescents.

Immunogenicity and protective efficacy of the HC009 mRNA vaccine against SARS-CoV-2.

With the rapid global spread of COVID-19 and the continuous emergence of variants, there is an urgent need to develop safe and effective vaccines. Here, we developed a novel mRNA vaccine, HC009, based on new formulation by the QTsome delivery platform. Immunogenicity results showed that the prime-boost immunization strategy with HC009 was able to induce robust and durable humoral immunity, as well as Th1-biased cellular responses in rodents or non-human primates (NHPs). After further challenge with live SARS-CoV-2 virus, HC009 provided adequate protection against virus infection in hACE2 transgenic mice. Therefore, HC009 could provide significant immune protection against SARS-CoV-2.

Comparison of long-term anti-RBD SARS-CoV-2 antibody response following different vaccination schemes in Tunisia.

AIM: The study aimed to compare long-term vaccine-induced humoral immunity following different vaccines regimens. METHODS: Anti-S-RBD total antibody levels were measured in blood samples of 167 participants nearly 6 months post-vaccination. Participants had received one; two or four doses of Pfizer vaccine or who received a third dose of mRNA vaccine (Pfizer) and primed with mRNA (Pfizer/Moderna), adenoviral (AstraZeneca/Jonson & Jonson) or inactivated (CoronaVac/Sinopharm) vaccine. RESULTS: Among all vaccination regimens, fourth dose of Pfizer achieved the highest S-RBD antibody titers. Nevertheless, the third dose of mRNA vaccine primed with adenoviral vaccine achieved the lowest titers of S-RBD antibody. Notably, the group that received a third dose of mRNA primed with two doses of mRNA vaccine exhibited higher S-RBD antibody compared to groups inoculated with a third dose of mRNA and primed with inactivated or adenovirus vaccine. CONCLUSION: Our data showed the superiority of three mRNA vaccinations compared to third heterologous vaccine (inactivated of adenoviral) including mRNA as booster in terms of humoral immunogenicity. Our findings supporting the use of additional booster shot from a more potent vaccine type such as mRNA vaccines. Nevertheless, due to the limited number of subjects, it is difficult to extrapolate the results of our study to the whole of Tunisian population. Future studies should investigate a larger cohort and other potential correlates of protection, such as cellular immunity and how it is affected by different vaccination schemes after long-term post-vaccination.

Incidence and risk factors of SARS-CoV-2 breakthrough infection in the early Omicron variant era among vaccinated and boosted individuals in Chicago.

BACKGROUND: SARS-CoV-2 vaccines are safe and effective against infection and severe COVID-19 disease worldwide. Certain co-morbid conditions cause immune dysfunction and may reduce immune response to vaccination. In contrast, those with co-morbidities may practice infection prevention strategies. Thus, the real-world clinical impact of co-morbidities on SARS-CoV-2 infection in the recent post-vaccination period is not well established. This study was performed to understand the epidemiology of Omicron breakthrough infection and evaluate associations with number of comorbidities in a vaccinated and boosted population. METHODS AND FINDINGS: A retrospective clinical cohort study was performed utilizing the Northwestern Medicine Enterprise Data Warehouse. Our study population was identified as fully vaccinated adults with at least one booster. The primary risk factor of interest was the number of co-morbidities. The primary outcome was the incidence and time to the first positive SARS-CoV-2 molecular test in the Omicron predominant era. Multivariable Cox modeling analyses to determine the hazard of SARS-CoV-2 infection were stratified by calendar time (Period 1: January 1 -June 30, 2022; Period 2: July 1 -December 31, 2022) due to violations in the proportional hazards assumption. In total, 133,191 patients were analyzed. During Period 1, having 3+ comorbidities was associated with increased hazard for breakthrough (HR = 1.16 CI 1.08-1.26). During Period 2 of the study, having 2 comorbidities (HR = 1.45 95% CI 1.26-1.67) and having 3+ comorbidities (HR 1.73, 95% CI 1.51-1.97) were associated with increased hazard for Omicron breakthrough. Older age was associated with decreased hazard in Period 1 of follow-up. Interaction terms for calendar time indicated significant changes in hazard for many factors between the first and second halves of the follow-up period. CONCLUSIONS: Omicron breakthrough is common with significantly higher risk for our most vulnerable patients with multiple co-morbidities. Age plays an important role in breakthrough infection with the highest incidence among young adults, which may be due to age-related behavioral factors. These findings reflect real-world differences in immunity and exposure risk behaviors for populations vulnerable to COVID-19.

Saponin nanoparticle adjuvants incorporating Toll-like receptor agonists drive distinct immune signatures and potent vaccine responses.

Over the past few decades, the development of potent and safe immune-activating adjuvant technologies has become the heart of intensive research in the constant fight against highly mutative and immune evasive viruses such as influenza, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and human immunodeficiency virus (HIV). Herein, we developed a highly modular saponin-based nanoparticle platform incorporating Toll-like receptor agonists (TLRas) including TLR1/2a, TLR4a, and TLR7/8a adjuvants and their mixtures. These various TLRa-saponin nanoparticle adjuvant constructs induce unique acute cytokine and immune-signaling profiles, leading to specific T helper responses that could be of interest depending on the target disease for prevention. In a murine vaccine study, the adjuvants greatly improved the potency, durability, breadth, and neutralization of both COVID-19 and HIV vaccine candidates, suggesting the potential broad application of these adjuvant constructs to a range of different antigens. Overall, this work demonstrates a modular TLRa-SNP adjuvant platform that could improve the design of vaccines and affect modern vaccine development.

A single-dose MCMV-based vaccine elicits long-lasting immune protection in mice against distinct SARS-CoV-2 variants.

Current vaccines against COVID-19 elicit immune responses that are overall strong but wane rapidly. As a consequence, the necessary booster shots have contributed to vaccine fatigue. Hence, vaccines that would provide lasting protection against COVID-19 are needed, but are still unavailable. Cytomegaloviruses (CMVs) elicit lasting and uniquely strong immune responses. Used as vaccine vectors, they may be attractive tools that obviate the need for boosters. Therefore, we tested the murine CMV (MCMV) as a vaccine vector against COVID-19 in relevant preclinical models of immunization and challenge. We have previously developed a recombinant MCMV vaccine vector expressing the spike protein of the ancestral SARS-CoV-2 (MCMVS). In this study, we show that the MCMVS elicits a robust and lasting protection in young and aged mice. Notably, spike-specific humoral and cellular immunity was not only maintained but also even increased over a period of at least 6 months. During that time, antibody avidity continuously increased and expanded in breadth, resulting in neutralization of genetically distant variants, like Omicron BA.1. A single dose of MCMVS conferred rapid virus clearance upon challenge. Moreover, MCMVS vaccination controlled two variants of concern (VOCs), the Beta (B.1.135) and the Omicron (BA.1) variants. Thus, CMV vectors provide unique advantages over other vaccine technologies, eliciting broadly reactive and long-lasting immune responses against COVID-19.

The Development of Epitope-Based Recombinant Protein Vaccines against SARS-CoV-2.

The COVID-19 pandemic continues to cause infections and deaths, which are attributable to the SARS-CoV-2 Omicron variant of concern (VOC). Moderna's response to the declining protective efficacies of current SARS-CoV-2 vaccines against Omicron was to develop a bivalent booster vaccine based on the Spike (S) protein from the Wuhan and Omicron BA.4/BA.5 strains. This approach, while commendable, is unfeasible in light of rapidly emerging mutated viral strains. PubMed and Google Scholar were systematically reviewed for peer-reviewed papers up to January 2024. Articles included focused on specific themes such as the clinical history of recombinant protein vaccine development against different diseases, including COVID-19, the production of recombinant protein vaccines using different host expression systems, aspects to consider in recombinant protein vaccine development, and overcoming problems associated with large-scale recombinant protein vaccine production. In silico approaches to identify conserved and immunogenic epitopes could provide broad protection against SARS-CoV-2 VOCs but require validation in animal models. The recombinant protein vaccine development platform has shown a successful history in clinical development. Recombinant protein vaccines incorporating conserved epitopes may utilize a number of expression systems, such as yeast (Saccharomyces cerevisiae), baculovirus-insect cells (Sf9 cells), and Escherichia coli (E. coli). Current multi-epitope subunit vaccines against SARS-CoV-2 utilizing synthetic peptides are unfeasible for large-scale immunizations. Recombinant protein vaccines based on conserved and immunogenic proteins produced using E. coli offer high production yields, convenient purification, and cost-effective production of large-scale vaccine quantities capable of protecting against the SARS-CoV-2 D614G strain and its VOCs.

Synthetic mRNAs Containing Minimalistic Untranslated Regions Are Highly Functional In Vitro and In Vivo.

Synthetic mRNA produced by in vitro transcription (ivt mRNA) is the active pharmaceutical ingredient of approved anti-COVID-19 vaccines and of many drugs under development. Such synthetic mRNA typically contains several hundred bases of non-coding "untranslated" regions (UTRs) that are involved in the stabilization and translation of the mRNA. However, UTRs are often complex structures, which may complicate the entire production process. To eliminate this obstacle, we managed to reduce the total amount of nucleotides in the UTRs to only four bases. In this way, we generate minimal ivt mRNA ("minRNA"), which is less complex than the usual optimized ivt mRNAs that are contained, for example, in approved vaccines. We have compared the efficacy of minRNA to common augmented mRNAs (with UTRs of globin genes or those included in licensed vaccines) in vivo and in vitro and could demonstrate equivalent functionalities. Our minimal mRNA design will facilitate the further development and implementation of ivt mRNA-based vaccines and therapies.

Redox Balance and Inflammatory Response in Follicular Fluids of Women Recovered by SARS-CoV-2 Infection or Anti-COVID-19 Vaccinated: A Combined Metabolomics and Biochemical Study.

To date, not many studies have presented evidence of SARS-CoV-2 infecting the female reproductive system. Furthermore, so far, no effect of the administration of anti-COVID 19 vaccines has been reported to affect the quality of oocytes retrieved from women who resorted to assisted reproduction technology (ART). The FF metabolic profiles of women who had been infected by SARS-CoV-2 before IVF treatments or after COVID-19 vaccination were examined by 1H NMR. Immunochemical characterization of proteins and cytokines involved in the redox and inflammatory pathways was performed. The increased expression of SOD2 and NQO1, the lack of alteration of IL-6 and CXCL10 levels, as well as the increased expression of CD39, suggested that, both sharing similar molecular mechanisms or proceeding along different routes, the redox balance is controlled in the FF of both vaccinated and recovered women compared to controls. The lower amount of metabolites known to have proinflammatory activity, i.e., TMAO and lipids, further supported the biochemical results, suggesting that the FF microenvironment is controlled so as to guarantee oocyte quality and does not compromise the outcome of ART. In terms of the number of blastocysts obtained after ICSI and the pregnancy rate, the results are also comforting.

Heterologous mRNA/MVA delivering trimeric-RBD as effective vaccination regimen against SARS-CoV-2: COVARNA Consortium.

Despite the high efficiency of current SARS-CoV-2 mRNA vaccines in reducing COVID-19 morbidity and mortality, waning immunity and the emergence of resistant variants underscore the need for novel vaccination strategies. This study explores a heterologous mRNA/Modified Vaccinia virus Ankara (MVA) prime/boost regimen employing a trimeric form of the receptor binding domain (RBD) of the SARS-CoV-2 spike (S) protein compared to a homologous MVA/MVA regimen. In C57BL/6 mice, the RBD was delivered during priming via an mRNA vector encapsulated in nanoemulsions (NE) or lipid nanoparticles (LNP), followed by a booster with a replication-deficient MVA-based recombinant virus (MVA-RBD). This heterologous mRNA/MVA regimen elicited strong anti-RBD binding and neutralizing antibodies (BAbs and NAbs) against both the ancestral SARS-CoV-2 strain and different variants of concern (VoCs). Additionally, this protocol induced robust and polyfunctional RBD-specific CD4 and CD8 T cell responses, particularly in animals primed with mLNP-RBD. In K18-hACE2 transgenic mice, the LNP-RBD/MVA combination provided complete protection from morbidity and mortality following a live SARS-CoV-2 challenge compared with the partial protection observed with mNE-RBD/MVA or MVA/MVA regimens. Although the mNE-RBD/MVA regimen only protects half of the animals, it was able to induce antibodies with Fc-mediated effector functions besides NAbs. Moreover, viral replication and viral load in the respiratory tract were markedly reduced and decreased pro-inflammatory cytokine levels were observed. These results support the efficacy of heterologous mRNA/MVA vaccine combinations over homologous MVA/MVA regimen, using alternative nanocarriers that circumvent intellectual property restrictions of current mRNA vaccine formulations.

Immune signature in vaccinated versus non-vaccinated aged people with COVID-19 pneumonia.

BACKGROUND: A definition of the immunological features of COVID-19 pneumonia is needed to support clinical management of aged patients. In this study, we characterized the humoral and cellular immune responses in presence or absence of SARS-CoV-2 vaccination, in aged patients admitted to the IRCCS San Raffaele Hospital (Italy) for COVID-19 pneumonia between November 2021 and March 2022. METHODS: The study was approved by local authorities. Disease severity was evaluated according to WHO guidelines. We tested: (A) anti-SARS-CoV-2 humoral response (anti-RBD-S IgG, anti-S IgM, anti-N IgG, neutralizing activity against Delta, BA1, BA4/5 variants); (B) Lymphocyte B, CD4 and CD8 T-cell phenotype; (C) plasma cytokines. The impact of vaccine administration and different variants on the immunological responses was evaluated using standard linear regression models and Tobit models for censored outcomes adjusted for age, vaccine doses and gender. RESULT: We studied 47 aged patients (median age 78.41), 22 (47%) female, 33 (70%) older than 70 years (elderly). At hospital admission, 36% were unvaccinated (VACno), whilst 63% had received 2 (VAC2) or 3 doses (VAC3) of vaccine. During hospitalization, WHO score > 5 was higher in unvaccinated (14% in VAC3 vs. 43% in VAC2 and 44% VACno). Independently from vaccination doses and gender, elderly had overall reduced anti-SARS-CoV-2 humoral response (IgG-RBD-S, p = 0.0075). By linear regression, the anti-RBD-S (p = 0.0060), B (p = 0.0079), CD8 (p = 0.0043) and Th2 cell counts (p = 0.0131) were higher in VAC2 + 3 compared to VACno. Delta variant was the most representative in VAC2 (n = 13/18, 72%), detected in 41% of VACno, whereas undetected in VAC3, and anti-RBD-S production was higher in VAC2 vs. VACno (p = 0.0001), alongside neutralization against Delta (p = 0141), BA1 (p = 0.0255), BA4/5 (p = 0.0162). Infections with Delta also drove an increase of pro-inflammatory cytokines (IFN-α, p = 0.0463; IL-6, p = 0.0010). CONCLUSIONS: Administration of 3 vaccination doses reduces the severe symptomatology in aged and elderly. Vaccination showed a strong association with anti-SARS-CoV-2 humoral response and an expansion of Th2 T-cells populations, independently of age. Delta variants and number of vaccine doses affected the magnitude of the humoral response against the original SARS-CoV-2 and emerging variants. A systematic surveillance of the emerging variants is paramount to define future vaccination strategies.

Atypical and non-classical CD45RBlo memory B cells are the majority of circulating SARS-CoV-2 specific B cells following mRNA vaccination or COVID-19.

Resting memory B cells can be divided into classical or atypical groups, but the heterogenous marker expression on activated memory B cells makes similar classification difficult. Here, by longitudinal analysis of mass cytometry and CITE-seq data from cohorts with COVID-19, bacterial sepsis, or BNT162b2 mRNA vaccine, we observe that resting B cell memory consist of classical CD45RB+ memory and CD45RBlo memory, of which the latter contains of two distinct groups of CD11c+ atypical and CD23+ non-classical memory cells. CD45RB levels remain stable in these cells after activation, thereby enabling the tracking of activated B cells and plasmablasts derived from either CD45RB+ or CD45RBlo memory B cells. Moreover, in both COVID-19 patients and mRNA vaccination, CD45RBlo B cells formed the majority of SARS-CoV2 specific memory B cells and correlated with serum antibodies, while CD45RB+ memory are activated by bacterial sepsis. Our results thus identify that stably expressed CD45RB levels can be exploited to trace resting memory B cells and their activated progeny, and suggest that atypical and non-classical CD45RBlo memory B cells contribute to SARS-CoV-2 infection and vaccination.

4th booster-dose SARS-CoV-2 heterologous and homologous vaccination in rheumatological patients.

Objective: to evaluate the immune response to the SARS-CoV-2 vaccines in adults with immune-mediated rheumatic diseases (IMRDs) in comparison to healthy individuals, observed 1-20 weeks following the fourth vaccine dose. Additionally, to evaluate the impact of immunosuppressive therapies, vaccination schedules, the time interval between vaccination and sample collection on the vaccine's immune response. Methods: We designed a longitudinal observational study conducted at the rheumatology department of Hospital de Copiapó. Neutralizing antibodies (Nabs) titers against the Wuhan and Omicron variant were analyzed between 1-20 weeks after administration of the fourth dose of the SARS-CoV-2 vaccine to 341 participants (218 IMRD patients and 123 healthy controls). 218 IMRD patients with rheumatoid arthritis (RA), psoriatic arthritis (PsA), ankylosing spondylitis (AS), systemic lupus erythematosus (SLE), systemic vasculitis (VS) and systemic scleroderma (SS) were analyzed. Results: Performing a comparison between the variants, Wuhan vs Omicron, we noticed that there were significant differences (p<0.05) in the level of the ID50, both for healthy controls and for patients with IMRDs. The humoral response of patients with IMRDs is significantly lower compared to healthy controls for the Omicron variant of SARS-CoV-2 (p = 0.0015). The humoral response of patients with IMRDs decreases significantly when the time interval between vaccination and sample collection is greater than 35 days. This difference was observed in the response, both for the Wuhan variant and for the Omicron variant. Conclusion: The IMRDs patients, the humoral response variation in the SARS-CoV-2 vaccine depends on doses and type of vaccine administered, the humoral response times and the treatment that these patients are receiving.

Tetanus-diphtheria vaccine can prime SARS-CoV-2 cross-reactive T cells.

Vaccines containing tetanus-diphtheria antigens have been postulated to induce cross-reactive immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which could protect against coronavirus disease (COVID-19). In this work, we investigated the capacity of Tetanus-diphtheria (Td) vaccine to prime existing T cell immunity to SARS-CoV-2. To that end, we first collected known SARS-CoV-2 specific CD8+ T cell epitopes targeted during the course of SARS-CoV-2 infection in humans and identified as potentially cross-reactive with Td vaccine those sharing similarity with tetanus-diphtheria vaccine antigens, as judged by Levenshtein edit distances (≤ 20% edits per epitope sequence). As a result, we selected 25 potentially cross-reactive SARS-CoV-2 specific CD8+ T cell epitopes with high population coverage that were assembled into a synthetic peptide pool (TDX pool). Using peripheral blood mononuclear cells, we first determined by intracellular IFNγ staining assays existing CD8+ T cell recall responses to the TDX pool and to other peptide pools, including overlapping peptide pools covering SARS-CoV-2 Spike protein and Nucleocapsid phosphoprotein (NP). In the studied subjects, CD8+ T cell recall responses to Spike and TDX peptide pools were dominant and comparable, while recall responses to NP peptide pool were less frequent and weaker. Subsequently, we studied responses to the same peptides using antigen-inexperienced naive T cells primed/stimulated in vitro with Td vaccine. Priming stimulations were carried out by co-culturing naive T cells with autologous irradiated peripheral mononuclear cells in the presence of Td vaccine, IL-2, IL-7 and IL-15. Interestingly, naive CD8+ T cells stimulated/primed with Td vaccine responded strongly and specifically to the TDX pool, not to other SARS-CoV-2 peptide pools. Finally, we show that Td-immunization of C57BL/6J mice elicited T cells cross-reactive with the TDX pool. Collectively, our findings support that tetanus-diphtheria vaccines can prime SARS-CoV-2 cross-reactive T cells and likely contribute to shape the T cell responses to the virus.

Immune Response to COVID-19 Vaccination in Elite Athletes.

Purpose: This study analyses the immune response of elite athletes after COVID-19 vaccination with double-dose mRNA and a single-dose vector vaccine. Methods: Immunoglobulin G (IgG) antibody titers, neutralizing activity, CD4 and CD8 T-cells were examined in blood samples from 72 athletes before and after vaccination against COVID-19 (56 mRNA (BNT162b2 / mRNA-1273), 16 vector (Ad26.COV.2) vaccines). Side effects and training time loss was also recorded. Results: Induction of IgG antibodies (mRNA : 5702 BAU/ml ; 4343 BAU/ml (hereafter: median), vector: 61 BAU/ml ; 52 BAU/ml, p<0.01), their neutralizing activity (99.7% ; 10.6%, p<0.01), and SARS-CoV-2 spike-specific CD4 T-cells (0.13% ; 0.05% ; p<0.01) after mRNA double-dose vaccines was significantly more pronounced than after a single-dose vector vaccine. SARS-CoV-2 spike-specific CD8 T-cell levels after a vector vaccine (0.15%) were significantly higher than after mRNA vaccines (0.02%; p<0.01). When athletes who had initially received the vector vaccine were boostered with an mRNA vaccine, IgG antibodies (to 3456 BAU/ml; p<0.01), neutralizing activity (to 100%; p<0.01), CD4 (to 0.13%; p<0.01) and CD8 T-cells (to 0.43%; p<0.01) significantly increased. When compared with dual-dose mRNA regimen, IgG antibody response was lower (p<0.01), the neutralizing activity (p<0.01) and CD8 T-cell (p<0.01) response higher and no significant difference in CD4 T-cell response (p=0.54) between the two regimens. Cumulative training loss (3 days) did not significantly differ between vaccination regimens (p=0.46). Conclusion: mRNA and vector vaccines against SARSCoV-2 appear to induce different patterns of immune response in athletes. Lower immune induction after a single-shot vector vaccine was clearly optimized by a heterologous booster. Vaccine reactions were mild and short-lived.