(1) Background: This study aimed to compare the immunogenicity of the mix-and-match CoronaVac/BNT162b2 vaccination to the homologous CoronaVac/CoronaVac regimen. (2) Methods: We conducted a simple-blinded randomized superiority trial to measure SARS-CoV-2 neutralization antibodies and anti-spike receptor binding domain (RBD) IgG concentrations in blood samples of participants who had received the first dose of CoronaVac vaccine followed by a dose of BNT162b2 or CoronaVac vaccine. The primary endpoint for immunogenicity was the serum-neutralizing antibody level with a percentage of inhibition at 90% at 21–35 days after the boost. A difference of 25% between groups was considered clinically relevant. (3) Results: Among the 240 eligible participants, the primary endpoint data were available for 100 participants randomly allocated to the mix-and-match group versus 99 participants randomly allocated to the homologous dose group. The mix-and-match regimen elicited significantly higher levels of neutralizing antibodies (median level of 96%, interquartile range (IQR) (95–97) versus median level of 94%, IQR (81–96) and anti-spike IgG antibodies (median level of 13,460, IQR (2557–29,930) versus median level of 1190, IQR (347–4964) compared to the homologous group. Accordingly, the percentage of subjects with a percentage of neutralizing antibodies > 90% was significantly higher in the mix-and-match group (90.0%) versus the homologous (60.6%). Interestingly, no severe events were reported within 30 days after the second dose of vaccination in both groups. (4) Conclusions: Our data showed the superiority of the mix-and-match CoronaVac/BNT162b2 vaccination compared to the CoronaVac/CoronaVac regimen in terms of immunogenicity, thus constituting a proof-of-concept study supporting the use of inactivated vaccines in a mix-and-match strategy while ensuring good immunogenicity and safety.

Pediatricians are among the most trusted sources of vaccine information for parents. We aimed, in this study, to describe the attitudes and practices of Tunisian pediatricians regarding non-National Immunization Schedule (NIS) vaccines, specifically the COVID-19 vaccination for children, and to identify factors associated with their willingness to recommend it. We conducted a national cross-sectional study among Tunisian pediatricians between July and October 2023 using a standardized questionnaire administered face-to-face. We calculated prevalence with 95% confidence intervals (95%CIs) and adjusted odds ratios (aOR) using multivariable logistic regression. Of 330 contacted pediatricians, 192 (58.2%) responded (mean age: 50.9 ± 12.9 years). The majority (89.1%, 95% CI: [84.6–93.5]) said that they recommend other vaccines that are not part of the NIS and 40.6% [33.7–47.6] declared their willingness to recommend the COVID-19 vaccination for children. The odds of pediatricians willing to recommend the COVID-19 vaccination for children were higher among those who believed that this vaccine would reduce school absenteeism (aOR = 2.3 [1.1–5.1]) and among those who have great confidence in the Ministry of Health’s recommendations regarding COVID-19 vaccination (aOR = 6.1 [2.2–16.9]). More than half of the pediatricians in Tunisia recommend other vaccines that are not part of the NIS but show hesitancy toward the COVID-19 vaccine. Thus, involving pediatricians in the decision-making process for childhood vaccination strategies is crucial.

Background: Allogeneic hematopoietic stem cell transplantation (ASCT) induces acquired immunodeficiency, potentially altering vaccine response. Herein, we aimed to explore the clinical tolerance and the humoral and cellular immune responses following anti-SARS-CoV-2 vaccination in ASCT recipients. Methods: A prospective, non-randomized, controlled study that involved 43 ASCT subjects and 31 healthy controls. Humoral response was investigated using the Elecsys^® test anti-SARS-CoV-2. Cellular response was assessed using the QFN^® SARS-CoV-2 test. The lymphocyte cytokine profile was tested using the LEGENDplex™ HU Th Cytokine Panel Kit (12-plex). Results: Adverse effects (AE) were observed in 69% of patients, encompassing pain at the injection site, fever, asthenia, or headaches. Controls presented more side effects like pain in the injection site and asthenia with no difference in the overall AE frequency. Both groups exhibited robust humoral and cellular responses. Only the vaccine transplant delay impacted the humoral response alongside a previous SARS-CoV-2 infection. Noteworthily, controls displayed a Th1 cytokine profile, while patients showed a mixed Th1/Th2 profile. Conclusions: Pfizer-BioNTech^® anti-SARS-CoV-2 vaccination is well tolerated in ASCT patients, inducing robust humoral and cellular responses. Further exploration is warranted to understand the impact of a mixed cytokine profile in ASCT patients.

Background/Objectives: Pregnancy is characterized by complex immunological adaptations that may increase susceptibility to infections, including SARS-CoV-2. Interleukin-6 (IL-6), a key pro-inflammatory cytokine, plays a crucial role in the immune response and has been strongly implicated in the pathogenesis of COVID-19. Genetic variations in the IL6 gene, particularly single-nucleotide polymorphisms (SNPs) in the promoter region, can modulate IL-6 expression and potentially influence individual susceptibility to viral infections. This study aimed to evaluate the relationship between promoter region IL6 gene polymorphisms and COVID-19 susceptibility, as well as the inflammatory response, in pregnant women. Methods: We enrolled in this study 204 pregnant women with evidence of SARS-CoV-2 infection in pregnancy and 134 pregnant women with no evidence of SARS-CoV-2 infection in the past. Genotyping was conducted for the two functional SNPs in the IL6 promoter region, rs1800796 and rs1800797, via Sanger sequencing, and for associations with COVID-19 susceptibility and IL-6 levels were analyzed. Results: No significant association was found between IL6 polymorphisms and COVID-19, IL-6 levels, age, or immunization status. IL-6 levels > 5 pg/mL were more frequent in SARS-CoV-2-negative pregnant women than in SARS-CoV-2-positive pregnant women (p = 0.032). Among vaccinated participants, IL-6 levels were significantly higher in SARS-CoV-2-negative pregnant women (p = 0.044), while no difference was observed in the unvaccinated group. Conclusions:IL6 polymorphisms rs1800797 and rs1800796 were not associated with infection susceptibility or IL-6 levels. These results highlight the complex immunological interplay between pregnancy, infection, and genetic background and support the need for further research in larger cohorts.