SARS-CoV-2 Seroepidemiology and Antibody Levels in Children during BA.5 Predominance Period (preprint)

This is a SARS-CoV-2 seroepidemiological study in pediatric population(0-16 years) during BA.5 Omicron predominance period in Athens metropolitan area. Serum samples were tested for SARS-CoV-2 nucleocapsid antibodies(Abs-N), representing natural infection during three sub-periods of BA.5 predominance: 01/05/2022-31/08/2022(period A), 01/09/2022-31/12/2022(period B) and July 2023(period C) and epidemiological data were collected. Additionally in period C Abs-N seronegative samples were tested for SARS-CoV-2 spike antibodies(Abs-S). A total of 878 children were tested (males:51.3%) with median age(IQR): 108(36-156) months and seropositivity during the 3 subperiods was: A:292/417(70%), B:288/356(80.9%), C:89/105(84.8%), P-value<0.001. SARS-CoV-2 seropositivity increased for from period A to C for 0-1-year (P-value: 0.044), 1-4 years (P-value: 0.028) and 6-12 years children (P-value: 0.003). Children 6-12y had the highest seroposi-tivity rates in all subperiods (A: 77.3%, B: 91.4% and C: 95.8%). A significant correlation of monthly SARS-CoV-2 median antibody titers with monthly seropositivity rates was detected (rs:0.812, P-value:0.008). During period C, an additional 12/105 (11.4%) Abs-S seropositive and Abs-N ser-onegative samples were detected and total seropositivity was estimated at 96.2% (101/105). The increased SARS-CoV-2 seropositivity detected in current seroepidemiology study illustrates a high exposure rate during BA.5 predominance period. These data could guide public health decisions regarding immunization strategies and protection measures.

Comparison οf Immune Responses Through Multiparametric T cell Cytokine Expression Profile Between Children With Convalescent COVID-19 Or Multisystem Inflammatory Syndrome (preprint)

The immunological pathways that cause Multisystem Inflammatory Syndrome after SARS-CoV-2 infection in children(MIS-C) remain under investigation. Aim of this study was to prospectively compare T-cell cytokine expression profile in unvaccinated children with acute MIS-C(MIS-C_A) before immunosuppression, convalescent MIS-C(one month after syndrome onset, MIS-C_C), convalescent COVID-19(one month after hospitalization) and healthy, unvaccinated controls. Intracellular expression of IL-4, IL-2, IL-17, IFN-γ, TNF-α and Granzyme B, post SARS-CoV-2-Spike antigenic mix stimulation of T cell subsets was analyzed by 13-colour Flow Cytometry. Twenty children with median age(IQR): 11.5(7.25-14) years were included in the study. From the comparison of the flow cytometry analysis of the 14 markers of MIS-C_A with the other 3 groups(MIS-C_C, post-COVID-19 and controls), significant differences were identified for: 1. CD4+IL-17+/million CD3+: 293.0(256.4-870.9) vs 50.7(8.4-140.5); P-value:0.03, vs 96.7(89.2-135.4); P-value:0.03 and vs 8.7(0.0-82.4); P-value:0.03, respectively, 2. CD8+IL-17+/million CD3+: 335.2(225.8-429.9) vs 78.0(31.9-128.9) vs 84.1(0.0-204.6) vs 33.2(0.0-114.6); P-value:0.05, respectively 3. CD8+IFN-γ+/million CD3+: 162.2(91.6-273.4) vs 41.5(0.0-77.4); P-value:0.03 vs 30.3(0.0-92.8); P-value:0.08, respectively. In children presenting with MIS-C one month after COVID-19 infection, T cells were found to be polarized towards IL-17 and IFN-γ production compared to those with uncomplicated convalescent COVID-19, a finding that could provide possible immunological biomarkers for MIS-C detection.

Evaluation of T cell responses with the QuantiFERON SARS-CoV-2 assay in individuals with 3 doses of BNT162b2 vaccine, SARS-CoV-2 infection, or hybrid immunity (preprint)

Cellular immunity after SARS-CoV-2 infection or immunization may be important for long-lasting protection against severe COVID-19 disease. We investigated cellular immune responses after SARS-CoV-2 infection and/or vaccination with an interferon (IFN)-γ release assay (QuantiFERON, QFN). In parallel, we measured SARS-CoV-2 anti-Nucleocapsid (Abs-N), anti-Spike (Abs-S) and Neutralizing (NAbs) antibodies against SARS-CoV-2 wild type and Omicron variant. We recruited 41 participants: unvaccinated children and adults and vaccinated uninfected or vaccinated convalescent adults. All vaccinated adults had received three doses of the BNT162b2 COVID-19 vaccine at 6.2–10.9 months prior to their inclusion to the study. All the unvaccinated participants were tested negative with QFN. Regarding the vaccinated population, 50% (8/16) of the vaccinated uninfected adults and 57.1% (8/14) of the vaccinated convalescent adults were tested positive. Among the QFN positive individuals, a reactive response to antigen (Ag) 1 (CD4+ epitopes) and to Ag2 (CD4+ and CD8+ epitopes), was detected in 68.8% (11/16) and 87.5% (14/16) respectively, while 56.3% (9/16) had a reactive response to both antigens. Additionally, Ag1 IFN-γ values correlated with Abs-S (P < 0.001) and NAbs against wild type (P = 0.039) levels, but not with NAbs against Omicron variant (P = 0.09) and Ag2 IFN-γ values correlated only with Abs-S levels (P = 0.009). The SARS-CoV-2 QFN assay did not detect T cellular responses in unvaccinated individuals and in a significant number of vaccinated individuals. Further comparative studies with different immunology assays are required to elucidate whether this is the result of waning immunity or low sensitivity of the assay.