Search Results (373)

Background. Lower respiratory tract infections remain a major cause of morbidity and mortality in infants worldwide. Newborns possess an immature immune system but acquire passive immunity through maternal antibodies transferred via the placenta (IgG) and breast milk (IgA). Maternal vaccination may enhance this protection. This study aimed to quantify antibody levels against respiratory viruses in serum and breast milk from lactating women. Methods. Serum and breast milk samples were collected from 26 lactating mothers. Antibody levels were measured using an indirect enzyme-linked immunosorbent assay (ELISA) targeting seven viral antigens: influenza A (A/Thailand, A/California), influenza B (B/Phuket, B/Austria), SARS-CoV-2 (Spike and receptor-binding domain, RBD) and RSV F pre-fusion protein. Antibody isotypes IgG, IgA and IgM were analysed. Results. Virus-specific IgG and IgA antibodies were detected in all samples. Breast milk showed the highest levels of IgA, whereas serum contained higher IgG levels. A moderate positive correlation was observed between serum and milk IgG. No correlation was found between serum IgG and milk IgA, but both levels were elevated. Conclusions. Breast milk and serum contain relatively high levels of antibodies against the tested respiratory viruses. The elevated levels of serum IgG and milk IgA indicate a coordinated defence between systemic and mucosal immunity in response to infections. The levels and correlation of specific isotypes point to the source of the antibodies: milk IgG probably originates from the blood, whereas milk IgA is produced locally. Full article

Understanding how clinical symptoms relate to immune responses during major variant transitions remains important for informing post-pandemic surveillance and vaccination strategies. This study compared symptom patterns and SARS-CoV-2-specific anti-RBD IgM and anti-S1 IgG antibody responses among vaccinated individuals infected during the pre-Omicron and Omicron-dominant periods, representing a key phase in the evolution of SARS-CoV-2 population immunity. A retrospective analysis of 216 confirmed COVID-19 cases was performed by evaluating 11 predefined symptoms together with anti-RBD IgM and anti-S1 IgG levels measured at Day-14 after symptom onset, corresponding to the period when humoral antibody responses are detectable following SARS-CoV-2 infection. Participants with breakthrough infection during the Omicron-dominant period reported fewer symptoms overall compared to the pre-Omicron period, with a median of three versus four symptoms, respectively. Cough was the most common symptom during the Omicron period (82.1%), followed by sore throat (81.4%) and fever (78.6%). In contrast, loss of taste or smell was significantly more frequent in the pre-Omicron period (64.8% versus 22.9%, p < 0.05). IgG levels were significantly higher during the Omicron period than during the pre-Omicron period, increasing by 42.3%, reflecting enhanced antibody responses likely driven by repeated exposure. A consistent association between cough and elevated IgG levels was observed in both periods (p < 0.05), suggesting an association between symptom presentation and the magnitude of the early humoral response. These findings suggest that while clinical symptom profiles evolved across a major SARS-CoV-2 variant transition, certain symptom–antibody relationships remained consistent. Such associations may provide insight into how clinical manifestations relate to immune responses in populations with pre-existing immunity and may support interpretation of symptomatic infection during ongoing SARS-CoV-2 circulation. Full article

Background: The emergence of SARS-CoV-2 variants necessitates the development of effective adjuvants to enhance subunit vaccine immunogenicity. Safe adjuvants are essential to enhance the immunogenicity of SARS-CoV-2 receptor-binding domain (RBD) subunit vaccines. Traditional Chinese medicine polysaccharides are attractive candidates due to their immunomodulatory properties. Methods: Female BALB/c mice (6–8 weeks) were immunized on days 0, 7, and 21 with an RBD protein (20 μg) alone or formulated with Poria cocos polysaccharide fraction PCP-I or PCP-II (200 μg), Isatis indigotica polysaccharide, or aluminum adjuvant; PBS served as a control. RBD-specific total IgG and subclasses were quantified by ELISA on day 7 after the third immunization. Neutralizing antibody titers were measured by a pseudovirus assay on days 14, 28, and 56 after the first immunization. Splenic CD19⁺ B cells were analyzed by flow cytometry, and antigen-stimulated IFN-γ and IL-4 spot-forming cells were quantified by ELISpot. Results: PCP-II significantly increased RBD-specific total IgG and IgG1 compared with RBD alone and other formulations, whereas IgG2a and IgG2b remained unchanged. Both PCP-I and PCP-II increased neutralizing titers versus RBD alone, and PCP-II showed an earlier and sustained increase in neutralizing responses through day 56. PCP-II showed a non-significant increase in splenic CD19⁺ B cell frequency. PCP-I and PCP-II markedly increased IFN-γ-secreting splenocytes without increasing IL-4, indicating enhanced antigen-specific cellular responses. Conclusion: In this comparative evaluation of traditional Chinese medicine polysaccharide candidates in a SARS-CoV-2 RBD subunit vaccine model, PCP-II showed the most prominent adjuvant activity. PCP-II enhanced antigen-specific humoral immunogenicity, improved neutralizing antibody responses, and was associated with increased IFN-γ-related cellular responses, supporting its potential as a candidate polysaccharide adjuvant for protein subunit vaccines. Full article

Background and Objectives: Healthcare workers are at heightened risk of SARS-CoV-2 infection. Understanding the duration and protective value of vaccine-induced immunity is critical to inform booster strategies. This study investigates longitudinal dynamics of anti-SARS-CoV-2 receptor-binding domain IgG (anti-RBD IgG) antibodies and their association with infection risk among vaccinated healthcare workers. Materials and Methods: A prospective cohort study was conducted at Vilnius University Hospital Santaros Klinikos, Lithuania. A total of 1778 healthcare workers who completed a primary COVID-19 vaccination series were followed. Blood samples were collected every three months to measure anti-RBD IgG levels. Participants also received up to three booster doses. COVID-19 was identified by PCR, antigen tests, or positive anti-nucleocapsid IgG. For serologically detected cases, infection timing was assigned to the interval between study visits. Antibody dynamics were analyzed across vaccination stages, time, age groups, and circulating SARS-CoV-2 variants. Results: Anti-RBD IgG titers peaked in the first quarter after primary vaccination (mean 7904 AU/mL), declined sharply by quarters 2–3, and rose substantially after booster doses. Following the first booster, titers increased to ~12,598 AU/mL in quarter 1 and continued rising through quarter 3. The highest levels were observed after the second booster (24,456 AU/mL in Q1), followed by gradual decline. A high-titer plateau persisted from quarters 6 to 9 (~21,000 AU/mL), followed by decline in quarters 10–11 and partial rebound in Q12. Approximately 49.6% of participants experienced COVID-19 during follow-up. Antibody response patterns were similar across age groups, with only minor transient differences. Conclusions: COVID-19 booster doses significantly enhance and prolong humoral immunity in healthcare workers compared with the primary vaccination series. However, antibody waning over time emphasizes the need for timely boosters, particularly during periods of variant circulation. These findings support continued booster vaccination and monitoring of long-term immune protection, although anti-RBD IgG should be interpreted as a surrogate marker of humoral rather than overall immunity. Full article

Background/Objective: This study is a cross-sectional investigation of long-term immune responses measured at different time intervals after COVID-19 infections, vaccinations, or combined exposure. The focus is on immune reactivity against recombinant spike (S) and nucleocapsid (N) protein antigens. Materials and Methods: Serum antibody levels were assessed up to four to four and a half years after infection or immunization, including virus-specific immunoglobulin G (IgG), IgA and IgM antibodies, as well as neutralizing antibodies against the S-protein. Cellular immunity was assessed by analyzing peripheral blood mononuclear cells (PBMC; n = 43 in first cohort, n = 32 in second cohort), including T-helper memory and cytotoxic subsets, and cytokine production after in vitro stimulation with recombinant SARS-CoV-2 proteins. A multiplex cytokine assay was used to analyze effector and regulatory immune responses. Results: Virus-specific IgG antibodies persisted for years after exposure to SARS-CoV-2, with IgG against the receptor-binding domain (RBD) correlating most strongly with neutralizing activity. Vaccinated individuals demonstrated higher IgA responses, whereas antibodies to the N-protein were associated with previous infection. No IgM antibodies were detected in any subjects, suggesting an immune response based on memory rather than ongoing infection. PBMCs from individuals with a history of both COVID-19 exposure and vaccination exhibited enhanced responsiveness, characterized by increased frequencies of memory T cells compared to vaccination alone. Stimulating with the S-protein induces higher cytokine production, including IFN-gamma, TNF-alfa, and IL-12(p70), compared with stimulation by the N-protein. Cytokines such as IL-10 and TGF-beta are also elevated, suggesting immune regulation rather than persistent inflammation. Conclusions: SARS-CoV-2 infection and vaccination are associated with persistent humoral and cellular immune responses detectable several years after exposure. Individuals with hybrid immunity exhibit broader and functionally enhanced immune reactivity, indicating more robust long-term immune memory. Future studies should focus on the long-term consequences of hybrid immunity and optimize other vaccine strategies, including recombinant antigen vaccines. Full article

Background/Objectives: Our previous study demonstrated that while the third SARS-CoV-2 booster effectively enhanced immunity against the Delta subvariant, its protection declined over time. This study aimed to evaluate and compare the humoral and cellular immune responses, as well as reactogenicity, of the mRNA-1273 vaccine administered as a fourth booster in healthy Thai adults previously vaccinated with two doses of CoronaVac (CV) followed by a third dose of either AZD1222 (AZ) or BNT162b2 (BNT). Methods: Participants received a single 100 µg (0.5 mL) intramuscular dose of mRNA-1273. Blood samples were collected at baseline (D0), D14, D90, and D180 to assess anti-RBD IgG, conduct a surrogate virus neutralization test (sVNT) against the Delta and Omicron variants, and assess IFN-γ levels and reactogenicity. Results: Both 2CV/AZ- and 2CV/BNT-primed groups exhibited comparable local and systemic reactogenicity. The fourth mRNA-1273 dose markedly increased Delta variant inhibition within 14 days in both groups and remained at high levels at Days 90 and 180. sVNT inhibition against Omicron rose similarly in both groups at Day 14; it declined sharply by Days 90 and 180, with the 2CV/AZ-primed group showing significantly lower levels than the 2CV/BNT-primed group. Baseline anti-RBD IgG levels were lower in the 2CV/AZ group (p = 0.003) but surpassed those of the 2CV/BNT group by Day 14, with no significant differences at later time points. IFN-γ responses followed a similar pattern to anti-RBD IgG Conclusions: A heterologous fourth mRNA-1273 booster in both 2CV/AZ- and 2CV/BNT-primed groups effectively enhances B-cell and T-cell responses against SARS-CoV-2. However, emerging variants such as Omicron may still pose challenges. The trial was registered with the Thai Clinical Trials Registry: the name of the registry: “The comparison of immune response to the 4th dose booster with mRNA-1273 COVID-19 vaccine in individuals who had received 2 doses of CoronaVac and booster with ChAdOx-1 or BNT162b2 COVID-19 vaccine”, TCTR20220205002 on 5 February 2022. Full article

Background: People living with HIV (PLWH) constitute a vulnerable population during the COVID-19 pandemic; however, it remains uncertain whether long-term suppressive antiretroviral therapy (ART) restores sufficient immune competence to support robust hybrid immunity. While vaccination followed by breakthrough infection—termed hybrid immunity—typically elicits potent humoral responses in immunocompetent individuals, the functional quality and breadth of these responses against evolving Omicron subvariants remain poorly characterized in PLWH. This study aimed to assess functional antibody responses, including neutralizing activity and Fc effector functions, in vaccinated and unvaccinated PLWH who experienced breakthrough infection with Omicron subvariants BA.4/5 or BF.7. Methods: We enrolled three cohorts between December 5 and December 20, 2022: 25 HIV-negative individuals with breakthrough infection (BTI-HC), 20 ART-experienced PLWH with breakthrough infection following three-dose COVID-19 vaccination (BTI-HIV), and 10 ART-experienced PLWH with primary infection without prior vaccination (PI-HIV). All HIV-positive participants were receiving suppressive ART with regimens based on non-nucleoside reverse transcriptase inhibitors or integrase strand transfer inhibitors for a median of 3.4 years. We measured receptor-binding domain (RBD)-specific IgG, neutralizing antibody titers against ancestral D614G, Delta, BA.1, BA.4/5, BF.7, XDV, KP.2, and KP.3 variants, and antibody-dependent cellular cytotoxicity (ADCC) responses. Results: Despite lower absolute CD4⁺ T cell counts, BTI-HIV participants mounted RBD-binding IgG, neutralizing antibody, and ADCC responses that were comparable to BTI-HC and significantly exceeded PI-HIV across all tested variants. Both breakthrough infection cohorts exhibited immunological imprinting, with higher neutralizing titers against ancestral D614G than infecting BA.4/5 or BF.7 variants. Emerging variants XDV, KP.2, and KP.3 demonstrated substantial neutralization escape in all groups. PI-HIV showed markedly diminished neutralization breadth and failed to generate enough responses against all tested Omicron strains. Conclusions: Suppressive ART enables PLWH to mount hybrid immunity—conferred by vaccination followed by BF.7 or BA.4/5 breakthrough infection—with neutralizing and ADCC responses comparable to HIV-negative individuals, and significantly exceeding those of unvaccinated PLWH with primary infection. This underscores the critical role of vaccination in establishing effective hybrid immunity in this population. However, we observed immunological imprinting, with higher titers against ancestral strains than against infecting variants, and substantial escape by emerging sublineages XDV, KP.2, and KP.3 across all groups. These findings support prioritizing updated variant-containing vaccines for HIV-positive populations and reinforce the essential role of vaccination in this vulnerable group. Full article

Background/objectives: SARS-CoV-2 antibodies wane after natural infections and vaccinations. COVID-19 booster vaccination enhances the durability and functionality of antibodies against emerging SARS-CoV-2 variants. Data on booster-induced antibody durability in sub-Saharan Africa remain sparse. Comparative analysis of vaccine-induced responses between heterologous and homologous vaccination regimens remains limited. This study evaluated longitudinal RBD-specific IgG responses following homologous and heterologous COVID-19 booster vaccination in previously vaccinated adults. Methods: Adults with prior mRNA or adenoviral-vectored vaccination were boosted with either Pfizer (mRNA) or Janssen (adenoviral-vectored) vaccines. Plasma IgG binding to Wuhan, Delta, and Omicron RBDs was measured pre-booster and at 3, 6, and 9 months. A total of 181 participants were enrolled between November 2022 and October 2023. Results: More than 60% of participants had detectable pre-booster RBD- and N-antigen-specific IgG. Booster vaccination substantially increased Wuhan-specific RBD-IgG at three months, with limited boosting of Delta and Omicron responses. Antibody levels waned to pre-booster concentrations by month nine. Heterologous boosting with a viral-vectored prime followed by Pfizer mRNA significantly enhanced both peak RBD-IgG levels and durability. Conclusions: These longitudinal data provide rare real-world evidence on booster immunogenicity in African adults and demonstrate that heterologous regimens confer a short- to intermediate-term advantage in antibody magnitude compared to a homologous regimen. This benefit was most pronounced within the first six months post-boost. The findings support additional booster dosing to strengthen protection against emerging variants in sub-Saharan Africa. Full article

The clinical severity of COVID-19 is influenced by cellular and humoral immune responses, as well as the dynamics of viral replication. In line with this, the current study examined systemic and mucosal immunity responses alongside viral load in unvaccinated SARS-CoV-2-infected individuals during the period of Omicron predominance. Between 2022 and 2023, when Omicron prevalence was at its peak, 48 SARS-CoV-2-positive cases with varied severity were recruited using positive PCR testing, and 48 negative controls were recruited using negative PCR testing at Moi Teaching and Referral Hospital, Kenya. Severe patients showed higher viral loads and systemic anti-spike IgG levels compared to moderate and asymptomatic individuals. Asymptomatic individuals had higher mucosal anti-spike IgG and receptor-binding domain (RBD) levels compared to severe patients. Systemic IFN-α mRNA transcripts were higher in asymptomatic individuals compared to patients with severe COVID-19 and healthy individuals. Severe patients had significantly lower expression of IFN-γ mRNA transcript levels in both blood and mucosa, as well as significantly lower systemic IFI-16 mRNA transcript levels. These findings reflect associations observed in a cross-sectional design and should not be interpreted as causal mechanisms. Suppressed interferon responses, both mucosal and systemic, were associated with severe disease. In conclusion, high systemic IgG and viral loads and low interferon responses were closely linked to severe COVID-19 outcomes. Full article

Autoimmune thyroiditis (AIT) is characterized by dysregulated endocrine–immune interactions, and vitamin D has been proposed as a potential immunomodulatory factor influencing vaccine-induced immune responses. This study investigated the association between serum vitamin D status and humoral responses to SARS-CoV-2 vaccination in patients with AIT, while exploring potential molecular mechanisms using network pharmacology, molecular docking and Molecular Dynamics (MD) simulations. Patients were stratified according to serum 25-hydroxyvitamin D levels as deficient, insufficient, or sufficient. Anti–spike receptor-binding domain (RBD) IgG titers, thyroid autoantibodies, and thyroid-stimulating hormone levels were measured. In parallel, vitamin D₃ related molecular targets were integrated with AIT-associated genes, followed by protein–protein interaction analysis, molecular docking and MD simulations were performed to assess the interactions between vitamin D₃ (cholecalciferol) and selected key proteins. An inverse correlation was observed between serum vitamin D levels and anti-RBD IgG titers (p = 0.0013), with higher antibody responses detected in vitamin D-deficient patients. Network pharmacology analysis highlighted CYP19A1, CYP17A1, and ESR1 as prioritized targets associated with steroid hormone biosynthesis and endocrine signaling pathways. Molecular docking showed compatible binding of vitamin D₃ to these proteins, while MD simulations supported the structural stability of the complexes over time. Collectively, these findings suggest that vitamin D status may influence post-vaccination humoral immune responses in AIT, potentially through modulation of endocrine–immune crosstalk. Further longitudinal and mechanistic studies are required to clarify causality and clinical relevance. Full article

Background/Objectives: SARS-CoV-2, the causative agent of COVID-19, has been responsible for more than seven million deaths worldwide since its emergence. The Bacillus Calmette–Guérin (BCG) vaccine, used for over 100 years to prevent tuberculosis, induces a Th1-prominent immune response that is important for protection against Mycobacterium tuberculosis, other mycobacteria, and intracellular pathogens. BCG has also been shown to induce innate immune memory and heterologous protection against non-related infections. Additionally, BCG has been used as a vector to express heterologous proteins, showing protective effects against various diseases, particularly respiratory viral infections, including SARS-CoV-2. In this report, we constructed two recombinant BCG strains as potential vaccine candidates based on the receptor-binding domain (RBD) of the Spike antigen: one expressing only the RBD protein (rBCG-RBD) and another expressing the RBD protein in fusion with the LTB (Escherichia coli Labile Toxin subunit B) adjuvant (rBCG-LTB-RBD). Methods: We evaluated the induction of SARS-CoV-2-specific humoral and cellular immune responses using these vaccine candidates in a prime–boost strategy with a booster dose using the rRBD protein (produced in cell culture) and the Alum adjuvant. Antisera were evaluated for neutralization of the Wuhan and Omicron SARS-CoV-2 pseudotyped virus. Results: Either immunization scheme (rBCG-RBD/rRBD or rBCG-LTB-RBD/rRBD) induced high IgG antibody titers, with antibody neutralization against a Wuhan SARS-CoV-2 pseudotyped virus after 10 weeks. The antibody levels induced by rBCG-RBD/rRBD were maintained for up to 9 months. Interestingly, only the sera from mice receiving the prime–boost with rBCG-LTB-RBD/rRBD showed cross-reactive neutralization against the Omicron SARS-CoV-2 pseudotyped virus. Immunization with rBCG-RBD or rBCG-LTB-RBD and a rRBD booster dose promoted the induction of specific CD4+ and CD8+ T cells producing Th1/Th2 cytokines (IL-4, TNF-α and IFN-γ). Conclusions: Our study highlights the potential of the prime–boost immunization strategy using rBCG-RBD/rRBD to induce long-term immunity and rBCG-LTB-RBD/rRBD to induce cross-protection against different variants, both of which could serve as promising vaccine candidates. Full article

Background/Objectives: The emergence of immune-evasive SARS-CoV-2 variants highlights the need for adaptable vaccine strategies. Trimeric receptor-binding domain (tRBD) antigens offer structural and immunological advantages over monomeric RBDs, but DNA vaccine efficacy has been limited by inefficient antigen expression, particularly in non-dividing antigen-presenting cells. Although cytoplasmic transcription–based DNA platforms have been developed to overcome nuclear entry barriers, their utility for antigen structure–function optimization remains underexplored. This study evaluated whether integrating a rationally designed trimeric RBD with a T7-driven cytoplasmic transcription system could enhance immunogenic performance. Methods: A DNA vaccine encoding a tandem trimeric SARS-CoV-2 RBD was delivered using a T7 RNA polymerase-driven cytoplasmic transcription system. In vitro antigen expression was assessed following Lipofectamine 3000-mediated transfection. In vivo, mice were immunized with the SM-102-based Rpol/tRBD/LNP formulation, and immunogenicity was assessed by antigen-specific antibody titers, serum neutralizing activity, and T-cell response profiling, together with basic safety/tolerability evaluations. Results: The T7-driven cytoplasmic transcription system markedly increased antigen mRNA and protein expression compared with conventional plasmid delivery. Rpol/tRBD vaccination induced higher anti-RBD IgG titers, enhanced neutralizing antibody activity, and robust CD8⁺ T cell responses relative to monomeric RBD and plasmid-based trimeric RBD vaccines. Immune responses were Th1-skewed and accompanied by germinal center activation without excessive inflammatory cytokine induction, body-weight loss, or hepatic and renal toxicity. Conclusions: This study demonstrates that integrating rational trimeric antigen engineering with direct cytoplasmic transcription enables balanced and well-tolerated immune activation in a DNA vaccine context. The T7 autogene-based platform provides a flexible framework for antigen structure–function optimization and supports the development of next-generation DNA vaccines targeting rapidly evolving viral pathogens. Full article

Background/Objectives: SARS-CoV-2 continues to generate antigenically divergent variants that reduce the breadth of existing vaccine-induced antibody responses. Fc-fusion subunit vaccines offer advantages in stability, antigen display, and Fc-mediated immune engagement. This study aimed to design and evaluate a tetravalent RBD–Fc fusion construct incorporating RBDs from Wuhan-Hu-1 and Omicron BA.4/BA.5 and to determine whether this configuration can induce broad antibody recognition across SARS-CoV-2 variants. The objective was to assess its feasibility, biochemical properties, and initial immunogenicity. Methods: Immune responses to the construct were first assessed using the C-ImmSim simulation platform. The full-length fusion was synthesized, subcloned into pcDNA3.1(+), expressed in HEK293 cells, and purified by Protein G affinity chromatography. Protein integrity was evaluated by reducing SDS–PAGE. BALB/c mice (female, 8 weeks) were immunized with a prime–boost–boost schedule, and sera were analyzed by ELISA, considering binding to Wuhan-Hu-1, Omicron BA.4/BA.5, and a panel of RBD variants. Results: In silico analysis predicted coordinated antigen clearance, class switching, memory B- and CD4⁺ T-cell formation, and transient cytokine induction. The recombinant protein was expressed efficiently, yielding a major ~56 kDa band and a ~23 kDa RBD fragment. Vaccinated mice generated strong IgG responses to Wuhan-Hu-1 and BA.4/BA.5 RBDs and showed broad binding to major variant RBDs. Conclusions: The tetravalent RBD–Fc fusion vaccine was successfully produced and elicited broad antibody binding across SARS-CoV-2 variants, supporting its potential as a versatile protein-based vaccine platform. Full article

Background: Antigen format strongly influences the immunogenicity of gene-based vaccines. Full-length Spike is widely used in licensed COVID-19 vaccines, while truncated subunits such as S1 or the receptor-binding domain (RBD) may simplify vector design but risk reduced potency. We aimed to compare these antigen formats in an AAV9 delivery platform. Methods: BALB/c mice were immunized intramuscularly with recombinant AAV9 encoding full-length Spike, S1, or RBD at doses of 1 × 10¹⁰ or 1 × 10¹¹ viral genomes. Immune responses were assessed by serology, virus neutralization, T-cell profiling, and histopathology. Results: All constructs expressed antigen in vitro and in vivo. Only full-length Spike elicited robust neutralizing antibodies at both doses, with titers rising significantly by week 12. High-dose RBD induced neutralization in a minority of animals, whereas S1 failed to do so. Antigen-specific IgG responses scaled with insert length (Spike > S1 > RBD). Cellular immunity was dominated by CD8⁺ effector memory T cells, strongest in the Spike group, which also induced measurable CD4⁺ responses. Local transient myositis was observed at the injection site but resolved by week 24, with no systemic pathology. Conclusions: Full-length Spike outperforms truncated subunits in the AAV context, highlighting antigen structure as a critical factor for next-generation coronavirus vaccine design. Full article

Background: Healthcare workers (HCWs) are at high risk of breakthrough SARS-CoV-2 infections despite complete vaccination schedules. There are gaps in our understanding of the specific antibody isotypes and cytokine profiles produced during an infection following vaccination. In this study, we evaluated SARS-CoV-2⁻specific antibody isotypes and their association with cytokine production in HCWs with breakthrough infections. Methods: Serum samples from 114 HCWs were analyzed for antibody isotypes against the nucleoprotein (NCP) and the receptor binding domain (RBD) of the spike protein, as well as for a panel of 13 cytokines. Results: Vaccinated SARS-CoV-2⁺ HCWs showed a higher prevalence of anti-SARS-CoV-2 antibodies against NCP (IgM = 93.8%, IgG = 93.8%, IgA = 28.1%) and RBD (IgM = 46.9%, IgG = 100%, IgA = 90.6%). A specific IgM response to NCP was more frequent in vaccinated SARS-CoV-2⁺ individuals, whereas IgA responses were predominantly specific for RBD. Both pro- and anti-inflammatory cytokines were elevated in vaccinated HCWs with breakthrough infections compared with unvaccinated and uninfected individuals. Interestingly, infected IgG+ HCWs with IgM specific for both NCP and RBD exhibited significantly higher IL-8, IL-6, TNF-α, IFN-γ, IL-2, IL-10, and TGF-β concentrations. Conclusion. Our data show that breakthrough infections in vaccinated HCWs induce a robust pro-and anti-inflammatory cytokine profile, which is associated with a broader IgM response directed against both NCP and RBD. Full article