Search Results (1,359)

Introduction: From 12 March 2020, when the first cases of COVID-19 were registered in Kosovo, to 9 March 2023, there were a total of 273,310 reported cases of COVID-19 and 3211 reported deaths in Kosovo (CFR: 1.17%). Health care workers (HCWs) have been at a higher risk of contracting SARS-CoV-2 infection; nevertheless, data on seroprevalence of SARS-CoV-2 antibodies among HCWs in Kosovo are very limited. Methodology: A cross-sectional serology study with 1654 healthcare professionals throughout Kosovo was conducted to determine the presence of antibodies against the spike antigen of SARS-CoV-2. In addition, a structured questionnaire was administered to study participants to obtain basic demographic data, and information on prior infection and COVID-19 vaccination status. Results: Antibodies against the spike antigen of SARS-CoV-2 were detected in almost all (99.8%) HCWs that participated in the study. The average antibody titer was 8030.8 AU/mL in women and 9533.7 AU/mL in men. Sixty-four percent of HCWs in this study reported prior infection with SARS-CoV-2, 6% of whom were hospitalized. Over 98% of study participants had received SARS-CoV-2 vaccination. Conclusions: Almost all HCWs participating in the study had antibodies against the spike antigen of SARS-CoV-2. This is most probably the result of the high COVID-19 vaccination rate in Kosovo as well as infection with SARS-CoV-2. Full article

Background: Humoral immune responses to SARS-CoV-2 are well documented, yet the immunopathogenic mechanisms distinguishing severe from critical disease remain incompletely defined, particularly in Middle Eastern populations. We investigated antibody responses across levels of clinical severity in a Saudi Arabian cohort. Methods: In this multicentre study, we analysed 406 participants stratified into five clinical groups: controls, asymptomatic, mild, severe, and critically ill requiring intensive care unit (ICU) admission. SARS-CoV-2-specific IgG and IgM levels were quantified alongside surrogate ACE2-RBD neutralisation activity. Associations between humoral markers, demographic factors, comorbidities, and disease severity were assessed. Results: SARS-CoV-2-specific IgG and IgM levels differed significantly across disease severity groups (p < 0.001), with higher levels observed in groups with greater clinical severity. No significant difference in IgG or IgM levels was observed between the severe and ICU groups (IgG p = 0.384; IgM p = 0.768). While binding antibody levels were associated with severity, surrogate ACE2-RBD neutralising activity did not differ significantly across groups (p = 0.209). Increasing age (χ² = 44.5) and the presence of comorbidities (χ² = 31.9) were associated with more severe clinical categories, whereas sex was not. Conclusions: These findings suggest that antibody levels provide useful information about exposure and immune activation, but antibody quantity alone does not fully explain the transition from severe to critical disease. The results support interpreting serological measures alongside clinical factors such as age and chronic illness. Full article

Background: The dynamics of humoral immune responses following primary and booster COVID-19 vaccinations are crucial to understand in order to optimize vaccination strategies. This study evaluates the magnitude and durability of SARS-CoV-2-specific IgG antibody responses across different vaccines in a large cohort of Bangladeshi adults. Methods: A total of 6300 adults from nine hospitals across eight divisions of Bangladesh were enrolled. Participants received two primary doses of either ChAdOx1 nCoV-19 (Covishield, Serum Institute of India, n = 2855), mRNA-1273 (Moderna, n = 578), BNT162b2 (Pfizer-BioNTech, n = 121), or Vero-cell-inactivated (Sinopharm, n = 2746) vaccines. Booster doses were administered at one-year intervals post-primary vaccination. SARS-CoV-2 spike receptor-binding domain (RBD)-specific IgG antibody responses were measured by ELISA using serum from vaccinees at multiple time points after two primary and two booster doses. Results: A total of 3745 individuals received booster 1 (third dose), with 59% receiving heterologous boosters (a different vaccine regimen than the primary doses). Only 5.5% (n = 347) of participants received a second booster one year after the first booster (among them, 99% received BNT162b2). Our results suggest that heterologous boosters with the mRNA vaccine induced higher IgG levels than homologous boosters for individuals who received primary vaccination with adenovirus vector-based ChAdOx1 nCoV-19 or a Vero-cell-inactivated vaccine. However, in those who initially received the mRNA-based vaccine, both homologous and heterologous boosters produced comparable IgG responses. Among all vaccine types, booster immunization with the Vero-cell-inactivated vaccine induced the lowest antibody responses. Longitudinal analysis demonstrated significantly high IgG levels over the 12 months following the first booster (p < 0.0001); however, IgG levels declined significantly after the second booster dose (fourth dose). Conclusions: Heterologous boosting strategies, particularly those involving mRNA vaccines, elicit stronger and more sustained IgG responses compared to a homologous booster. However, antibody waning after the second booster highlights the need for continued monitoring and potential additional vaccine strategies. Full article

Background: Post-COVID syndrome represents a significant medical and public health challenge, particularly among older adults and individuals with type 2 diabetes mellitus (T2DM), in whom disturbances in immune and metabolic homeostasis may contribute to the development and persistence of symptoms following SARS-CoV-2 infection. Objective: To investigate the clinical, immunological, and metabolic characteristics of post-COVID syndrome in older adults with T2DM. Methods: A cross-sectional comparative study was conducted involving 141 patients aged ≥ 60 years who were evaluated more than one year after SARS-CoV-2 infection. Clinical data, anthropometric measurements, complete blood count parameters, biochemical markers, glycated hemoglobin (HbA1c), and SARS-CoV-2-specific IgG antibodies were assessed. Statistical analyses were performed using nonparametric methods, while Pearson’s χ² test was applied for categorical variables. A p-value < 0.05 was considered statistically significant. Results: Symptoms consistent with post-COVID syndrome one year after SARS-CoV-2 infection were identified in 53.2% of participants. No significant differences in anthropometric characteristics, hematological parameters, or most biochemical markers were observed between patients with and without post-COVID syndrome. Patients with T2DM exhibited higher fasting glucose, HbA1c, and SARS-CoV-2–specific IgG antibody levels, reflecting underlying metabolic characteristics and differences in humoral immune responses during the late post-COVID period. Conclusions: Post-COVID syndrome symptoms were frequently observed among older adults at the time of assessment, more than one year after SARS-CoV-2 infection, despite normalization of most laboratory parameters. In patients with T2DM, higher glucose, HbA1c, and antibody levels likely reflect underlying metabolic characteristics rather than a direct effect of post-COVID syndrome. Further longitudinal studies are warranted to clarify the long-term clinical significance of the observed metabolic and immunological findings. Full article

Background: Although prolonged inflammatory symptoms are an infrequent and problematic adverse effect of vaccination that can occur in some people, the transient activation of acute phase reactants (APRs) is expected with adjuvanted vaccines and helps to potentiate immune responses. Methods: This experiment examined the association between vaccine reactogenicity and immunogenicity in monkeys immunized with an adjuvanted recombinant protein including a receptor binding domain–human IgG1-Fc fusion protein (RBD-Fc) sequenced from the ancestral Wuhan strain of SARS-CoV-2. The acute inflammatory reaction to immunization was assessed by determining the decline in serum iron levels at 24 h and the increase in the neutrophil-to-lymphocyte ratio (NLR) as the adherent neutrophil pool trafficked into circulation. Results: Robust primary and secondary antibody responses were elicited. Larger decreases in serum iron and higher NLRs were associated with a stronger inhibition of RBD binding with angiotensin-converting enzyme (ACE2) when five early viral variants of SARS-CoV-2 were tested, including Wuhan, Alpha, Beta, Gamma and Delta. Inhibition of ACE2-RBD binding was less evident when the Omicron variant was tested. Individual variation in the APR was also predictive of the persistence of cell-mediated immunity based on the number of interferon-expressing mononuclear cells activated by viral antigen in ELISpot assays. Conclusions: Rapid antibody responses to primary immunization and large secondary responses to booster immunizations were elicited by this adjuvanted recombinant RBD-Fc vaccine, and our analysis affirmed the view that a transient APR can enhance antibody binding with antigen proteins. Full article

Background/Objectives: In the first months of their life, infants rely on maternal antibodies for immune protection. Breastmilk is a major source of these defenses, supplying secretory IgA, IgG, and IgM that help guard mucosal surfaces against pathogens such as SARS-CoV-2. Most studies on breastmilk immunity in the context of COVID-19 have emphasized circulating monomeric IgA, rather than the multimeric secretory IgA (sIgA) that is active at mucosal barriers. This study assessed in-depth the contribution of breastmilk antibody subtypes to SARS-CoV-2 neutralization capacity and how these profiles differ following maternal COVID-19 infection versus vaccination during pregnancy or postpartum. Methods: In this prospective cohort study, breastmilk samples were collected longitudinally from individuals who had COVID-19 during pregnancy or received COVID-19 mRNA vaccination during pregnancy or postpartum. Serological assays measured IgG, IgM, systemic IgA, and secretory IgA against SARS-CoV-2 spike and nucleocapsid antigens. Results: COVID-19 infection during pregnancy resulted in significantly higher systemic and secretory IgA levels compared to vaccination. Secretory IgA demonstrated a strong correlation with neutralization capacity. Principal component analysis revealed distinct antibody profiles in COVID-19-exposed individuals versus vaccinated cohorts, with significant overlap between pregnancy and postpartum vaccination groups. Conclusions: Although both COVID-19 vaccination and disease elicit sustained COVID-19-related antibodies in breastmilk, COVID-19 infection elicits a broader and more diverse antibody response in breastmilk, specifically with a greater secretory IgA generation. These findings support the value of maternal vaccination to safely confer mucosal immunity to neonates and the need for optimized vaccine formulations for mucosal immunity. Full article

Background/Objectives: The induction of anti-SARS-CoV-2 antibodies by COVID-19 vaccination reduces morbidity and mortality, but immune responses may be compromised in people living with HIV (PLWH). The aims of the current study were to determine whether viral suppression (VS) or immune reconstitution (IR) in PLWH directly affected their ability to produce effective levels of anti-SARS-CoV-2 antibodies in mucosal secretions or blood induced by vaccination. Methods: Anti-SARS-CoV-2 spike IgG, IgA and secretory IgA (SIgA) antibodies and their avidities were measured by ELISA in HIV-negative healthy controls (HC; n = 49) and PLWH (n = 94) using stimulated oral fluid (SOF) and serum. Frequencies of CD4/CD8 T cells and their expression of exhaustion/senescence were determined by flow cytometry. Cytokine levels were measured by cytokine bead arrays. Results: We showed that higher HIV burden negatively impacted the levels of systemic and mucosal anti-SARS-CoV-2 spike IgG antibodies produced. This differential IgG antibody production was unaffected by IR status, antiretroviral therapy duration or T cell exhaustion/senescence. PLWH elicited higher anti-SARS-CoV-2 spike IgA antibodies both in peripheral blood and oral mucosa and highr secretory IgA (SIgA) antibodies in the oral mucosa. PLWH with higher HIV RNA copies elicited lower IgG avidity but the IgA avidity indices remained unaffected. PLWH expressed higher levels of innate immunity cytokines in the oral mucosa, irrespective of the HIV RNA copies. Conclusions: Significantly fewer breakthrough infections in PLWH compared with HC, along with high IgA/SIgA antibodies and increased innate immunity cytokines in the SOF, suggest a potential role for mucosal immunity in the immunopathogenesis of COVID-19. Full article

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

Background: Following a significant decline during the 2020–2021 SARS-CoV-2 pandemic, Mycoplasma pneumoniae (MP) experienced a resurgence across Europe in 2023–2024. Although macrolide-resistant MP has increased globally, severe disease can occur even in the absence of resistance, which highlights the importance of rapid molecular characterization for clinical purposes. In this context, clinical severity is often improperly used as a surrogate marker of macrolide resistance, potentially driving unnecessary antibiotic escalation. Methods: We report a severe MP pneumonia occurring during the 2023–2024 resurgence and evaluate macrolide resistance through a rapid two-step workflow (Real Time-PCR screening for A2063G/A2064G followed by confirmatory 23S rRNA sequencing), to assess whether severity predicts resistance and to support antibiotic stewardship. Results: The patient developed acute hypoxic respiratory failure (PaO₂ 54.9 mmHg; P/F ratio 110), extensive centrilobular micronodules on chest CT imaging, significant systemic inflammation and elevated liver enzymes. Respiratory support was escalated from a Venturi mask to a high-flow nasal cannula and BiPAP. MP infection was confirmed by multiplex Real Time-PCR (RT-PCR) and supported by positive IgM/IgG serology. RT-PCR targeting A2063G/A2064G mutations revealed no resistance-associated variants, and Sanger sequencing of an 807 bp 23S rRNA fragment confirmed a wild-type genotype. Despite severe hypoxemic respiratory failure, no resistance-associated variants were detected, documenting a clear severity–genotype mismatch. Clinical and radiological improvement followed second-line antibiotic therapy. Conclusions: Severe MP pneumonia can occur despite the absence of macrolide resistance. During MP re-emergence, clinical severity should not be used to infer macrolide resistance. Integrating nucleic acid amplification test (NAAT) diagnosis with rapid genotyping/confirmatory 23S rRNA sequencing can prevent misclassification, reduce unwarranted broad-spectrum escalation, and strengthen antimicrobial stewardship decisions. Full article

Understanding the molecular mechanisms underlying host immune responses to SARS-CoV-2 vaccination remains essential, particularly in populations with a high prevalence of obesity. In this cross-sectional study, we evaluated whether body mass index (BMI) is associated with vaccine-induced humoral immunity in a cohort from northeastern Mexico and discuss the findings within a structural immunology framework of spike antigenicity and antibody–epitope interactions. A total of 138 adults were recruited in Reynosa and Matamoros (June 2021–June 2022) and categorized as healthy weight, overweight, or obese according to BMI criteria. Serum anti-SARS-CoV-2 IgG was assessed using an ELISA-based assay, and differences across BMI groups were tested using the Kruskal–Wallis approach. Among all participants, 33.3% were classified as obese and 99.3% (137/138) were seropositive for anti-SARS-CoV-2 IgG. No significant differences in IgG levels were detected between BMI categories (p = 0.20). These results indicate that, in this Mexican cohort—sampled during a period of heterogeneous and often incomplete vaccination schedules—obesity was not associated with reduced detectable anti-SARS-CoV-2 IgG responses. Our findings support the need to integrate population-level serology with mechanistic studies that interrogate antibody quality (e.g., neutralization potency and epitope specificity) to better connect clinical determinants such as obesity with molecular correlates of protection. 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: Despite hybrid and vaccine-induced immunity, SARS-CoV-2 continues to cause disease. The characterization of humoral and cellular immune responses is essential for guiding prevention strategies and booster dose policies; Methods: A prospective cohort study was conducted with 131 hospitalized patients with confirmed COVID-19 in the Aburrá Metropolitan Valley, Colombia. Clinical and immunological data were evaluated on days 1–3, days 5–7, days 8–12, and 4–5 months after diagnosis. Humoral immunity was assessed by enzyme-linked immunosorbent assay (ELISA), chemiluminescent microparticle immunoassay (CMIA), and neutralization testing, and cellular immunity by CD4⁺/CD8 T-cell responses. Results: vaccinated patients had higher baseline levels of IgG and neutralizing antibody positivity than unvaccinated patients (ELISA 89.1% vs. 60.0%; CMIA 86.4% vs. 50.0%; neutralizing antibodies 88.2% vs. 65.0%), but cases of severe disease occurred in both groups. Adults aged ≥65 years had higher antibody positivity, but severe disease persisted. Mortality at 28 days was 7.6%, mainly among critically ill patients with comorbidities. Antibodies persisted at 4–5 months but were lower in those with severe acute disease. Those who received the booster dose showed stronger CD4⁺/CD8⁺ activation (notably against the Omicron variant) than unvaccinated/partially vaccinated patients. Conclusions: Vaccination improved humoral and cellular responses, but severe breakthrough infections still occurred, particularly in high-risk patients. 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