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

Stronger and durable SARS-CoV-2 immune response to mRNA vaccines in 5-11 years old children with prior COVID-19

BACKGROUND AND OBJECTIVES

mRNA vaccines elicit a durable humoral response to SARS-CoV-2 in adults, whereas evidence in children is scarce. This study aimed to assess the early and long-term immune response to the mRNA vaccine in children with or without previous SARS-CoV-2 infection.

METHODS

In a multicentre prospective observational study, we profiled the immune response to the Pfizer BioNTech (BNT162b2) vaccine in 5-11-year-old children attending the University Pediatric Hospital of Padua and Bambino-Gesù Hospital in Rome (Italy) from December-2021 to February-2023. Blood samples were collected pre-, 1-, and 6-months after vaccination. Neutralizing antibodies (NAbs) and anti-spike-receptor-binding-domain (anti-S-RBD) IgG titers were analyzed through Plaque Reduction Neutralization Test (PRNT) and chemiluminescent immune-enzymatic assay (CLIA), respectively. Immune cell phenotypes were analyzed by flow cytometry.

RESULTS

Sixty children (26 [43 %] female, median age = 8 years [IQR = 7-10.7]) were enrolled in the study, including 46 children with a laboratory-confirmed previous COVID-19 (SARS-CoV-2-recovered) and 14 SARS-CoV-2-naïve participants defined as the absence of antigen-specific antibodies before vaccination. SARS-CoV-2-recovered participants recorded higher anti-S-RBD IgG and Wild-type and Omicron BA.2 NAbs titers than SARS-CoV-2-naïve participants at both 1- and 6-months after vaccination. Antibody titers correlated with T (Tregs) and B (Bregs) regulatory cell frequencies in SARS-CoV-2-recovered children. Both SARS-CoV-2-recovered and SARS-CoV-2-naïve participants decreased antibody titers by approximately 100 to 250 % from 1 to 6 months. While children with immunocompromising underlying conditions developed immune responses comparable to those of healthy children, solid organ transplant recipients exhibited lower levels of NAbs and anti-S-RBD IgG titers, as well as reduced frequencies of Tregs and Bregs.

CONCLUSIONS

mRNA vaccination triggered a higher production of specific anti-SARS-CoV-2 antibodies along with increased levels of regulatory cells in children with previous SARS-CoV-2 infection up to the following 6 months. These findings provide insights into boosting pre-existing immunity.

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.