COVID-19 mRNA BNT162b2 vaccine immunogenicity among children with a history of paediatric multisystem inflammatory syndrome temporally associated with COVID-19 (PIMS-TS).

We conducted a prospective cohort study of 20 patients with a history of paediatric multisystem inflammatory syndrome temporally associated with COVID-19 (PIMS group, median age seven years, 70% male) and 34 healthy controls without such a history (CONTROL group, median age eight years, 38% male) aged 5-12 years, to assess the immunogenicity of Pfizer-BioNTech COVID-19 mRNA BNT162b2 vaccine (Comirnaty®). Patients received two doses of COVID-19 mRNA BNT162b2 vaccine (10 ug/dose) 21 days apart. Pre-vaccine anti-S SARS-CoV-2 IgG antibodies were measured on the day of the first dose and at the median of 23 days after the second dose. The study was conducted during the COVID-19 wave dominated by the Omicron variant of the virus. Anti-NCP SARS-CoV-2 IgG antibodies were measured twice to evaluate incidents of infection during the study period. Pre-vaccine quantification of both types of antibodies allowed us to differentiate patients into COVID-19 naive and previously infected in order to compare hybrid immunity with vaccine-induced immunity. Before vaccination, anti-S IgG serum geometric mean concentration (GMC) was 61.17 BAU/ml in the PIMS group and 24.97 in the CONTROL group, while post-vaccination GMC was 3879.14 BAU/ml and 3704.87 BAU/ml, respectively, and did not significantly differ between the groups. Hybrid immunity (regardless of PIMS history) resulted in a higher concentration of SARS-CoV-2 anti-S antibodies after vaccination. Four (20%) of the children in the PIMS group and 11 (32%) in the CONTROL group got infected with SARS-CoV-2 during the study period, yet all of them asymptomatically, and this event has not significantly altered post-vaccination anti-S titers. In conclusion, COVID-19 vaccination was highly immunogenic in children, including those with a history of PIMS-TS; hybrid immunity overperforms vaccine-induced immunity in terms of serological response in children. However, vaccination effectiveness in preventing SARS-CoV-2 infections in children should be further evaluated.

COVID-19 mRNA BNT162b2 vaccine safety and B-cell and T-cell reactogenicity among children with a history of paediatric multisystem inflammatory syndrome temporally associated with COVID-19 (PIMS-TS) - preliminary study.

To assess the safety of Pfizer-BioNTech COVID-19 mRNA BNT162b2 vaccine (Comirnaty®) among patients with the anamnesis of paediatric inflammatory syndrome temporally associated with COVID-19 (PIMS-TS), we conducted a prospective cohort study of 21 patients with history of PIMS (PIMS group, median age 7.4 years, 71% male) and 71 healthy controls without such an anamnesis (CONTROL group, median age 9.0 years, 39% male) aged 5-18 years. Among them, 85 patients (all PIMS patients and 64 CONTROL patients) completed the two dose schedule of vaccination administered 21 days apart and 7 children in the CONTROL group received a single, age appropriate dose of a COVID-19 mRNA BNT162b2 vaccine during the study period. The frequency and character of reported adverse events (AEs) after each dose and results of flow cytometry (FC) 3 weeks after a second dose were compared between those groups. COVID-19 mRNA BNT162b2 vaccine safety profile was very good and comparable in both groups. No severe AEs were observed. 30% of all patients reported some general AE after any vaccine dose and 46% - some local AE. Frequency of reported AEs did not differ between groups except for local hardening at injection site, more common in PIMS group (20% vs 4% after any vaccine dose, p = 0,02). All AEs were benign, general AEs lasted up to 5 days and localised - up to 6 days after a vaccine dose. COVID-19 mRNA BNT162b2 vaccine did not induce any PIMS-like symptoms in any patient. We did not observe any significant T cells or B cells subset abnormalities in the PIMS group compared to the CONTROL group three weeks after a second dose except for terminally differentiated effector memory T cells that were higher in PIMS group (p < 0.0041). To sum up COVID-19 mRNA BNT162b2 vaccine in children with PIMS-TS was safe. Further studies are required to support our findings.