Assessment of SARS-CoV-2 immunity in convalescent children and adolescents (preprint)

Background: Persistence of protective immunity for SARS-CoV-2 is important against reinfection. Knowledge on SARS-CoV-2 immunity in pediatric patients is currently lacking. We opted to assess the SARS-CoV-2 adaptive immunity in recovered children and adolescents, addressing the pediatrics specific immunity towards COVID-19. Method: Two independent assays were performed to investigate humoral and cellular immunological memory in pediatric convalescent COVID-19 patients. Specifically, RBD IgG, CD4+, and CD8+ T cell responses were identified and quantified in recovered children and adolescents. Results: : SARS-CoV-2-specific RBD IgG detected in recovered patients had a half-life of 121.6 days and estimated duration of 7.9 months compared with baseline levels in controls. The specific T cell response was shown to be independent of recovery time. Both CD4+ and CD8+ T cells showed robust responses not only to spike (S) peptides (a main target of vaccine platforms) but were also similarly activated when stimulated by membrane (M) and nuclear (N) peptides. Importantly, we found the differences in the adaptive responses were correlated with the age of the recovered patients. The CD4+ T cell response to SARS-CoV-2 S peptide in children aged <12 years correlated with higher SARS-CoV-2 RBD IgG levels, whereas higher level of CD8+ T cells in children aged ≥12 years, suggesting the importance of a T cell-dependent humoral response in younger children under 12 years. Conclusion: Both cellular and humoral immunity against SARS-CoV-2 infections can be induced in pediatric patients. Our important findings provide fundamental knowledge on the immune memory responses to SARS-CoV-2 in recovered pediatric patients.

Effectiveness of BNT162b2 and CoronaVac in children and adolescents against SARS-CoV-2 infection during Omicron BA.2 wave in Hong Kong (preprint)

The SARS-CoV-2 Omicron BA.2 subvariant replaced BA.1 globally in early 2022, and caused an unprecedented tsunami of cases in Hong Kong, resulting in the collapse of elimination strategy. Vaccine effectiveness (VE) of BNT162b2 and CoronaVac against BA.2 is unclear. We utilize an ecological design incorporating population-level vaccine coverage statistics and territory-wide case-level SARS-CoV-2 infection surveillance data, and investigate the VE against infection during the Omicron BA.2 wave between January 1 to April 19, 2022, in Hong Kong for children and adolescents. We estimate VE to be 33.0% for 1 dose of BNT162b2 in children aged 5–11 and 40.8% for 2 doses of CoronaVac in children aged 3–11. We also estimate 54.9% and 86.8% VE for 2 and 3 doses of BNT162b2, and 55.0% and 92.0% VE for 2 and 3 doses of CoronaVac in adolescents aged 12–18. Our findings support preserved VE against infection by variants of concerns for children and adolescents in settings with extremely low levels of prior SARS-CoV-2 circulation.

Safety and Immunogenicity of 3 Doses of BNT162b2 and CoronaVac in Children and Adults with Inborn Errors of Immunity (preprint)

Background: Safety and immunogenicity of 3 doses of BNT162b2 and CoronaVac in adult and pediatric patients with inborn errors of immunity (IEIs) remain unknown. Intradermal vaccination may improve immunogenicity in immunocompromised patients. Our study (NCT04800133) aimed to determine the safety and immunogenicity in patients with IEIs receiving a 3-dose primary series of mRNA vaccine BNT162b2 (age 12+) or inactivated whole-virion vaccine CoronaVac (age 3+) in Hong Kong, including Omicron BA.1 neutralization, in a nonrandomized manner. Intradermal vaccination was also studied. Methods Thirty-nine patients were vaccinated, including 16 with homologous intramuscular 0.3ml BNT162b2 and 17 with homologous intramuscular 0.5ml CoronaVac. Two patients received 3 doses of intradermal 0.5ml CoronaVac, and 4 patients received 2 doses of intramuscular BNT162b2 and the third dose with intradermal BNT162b2. Adverse reactions and adverse events were tracked for 7 and 28 days after each dose. Antibody responses assessed included binding IgG antibody to wild-type (WT) spike receptor-binding domain (S-RBD IgG) and surrogate neutralization activity to WT and BA.1 viruses. T cell responses were examined by intracellular cytokine staining following stimulation with SARS-CoV-2 peptide pool(s). Results No safety concerns were identified. Inadequate antibody responses were found after 2 doses in patients with humoral immunodeficiencies and especially so against BA.1. Dose 3 of either vaccine increased S-RBD IgG response. T cell responses against SARS-CoV-2 antigens were detected in vaccinated IEI patients. Intradermal third dose vaccine led to high antibody response in 4 patients. Conclusions The primary vaccination series of BNT162b2 and CoronaVac in adults and children with IEIs should include 3 doses for optimal immunogenicity.

Immunogenicity and reactogenicity of SARS-CoV-2 mRNA and inactivated vaccines in healthy adolescents (preprint)

For SARS-CoV-2 vaccines, efficacy data for BNT162b2 but not CoronaVac are available in adolescents. Phase II/III studies focused on neutralizing antibody responses in adolescents, neglecting binding antibody and cellular responses that are also important against SARS-CoV-2. Therefore, we conducted a registered clinical study (NCT04800133) to establish immunobridging with various antibody and cellular immunity markers and to compare the immunogenicity and reactogenicity of these 2 vaccines in healthy adolescents. One-dose BNT162b2 outcomes were also assessed since it had been recommended in some localities due to the risk of myocarditis. Antibodies and T cell immune responses were non-inferior or similar in adolescents receiving 2 doses of BNT162b2 (BB, N=116) and CoronaVac (CC, N=123) versus adults after 2 doses of the same vaccine (BB, N=147; CC, N=141) but not in adolescents after 1 dose of BNT162b2 (B, N=116). CC induced SARS-CoV-2 nucleocapsid (N) and N C-terminal domain seroconversion in more adolescents than adults. Adverse reactions were mostly mild for both vaccines and more frequent for BNT162b2. We confirmed higher S, neutralizing, avidity and Fc receptor-binding antibody responses in adolescents receiving BB than CC. This is the first study to show similar induction of strong S-specific T cells by the 2 vaccines, in addition to N- and M-specific T cells induced by CoronaVac but not BNT162b2 in adolescents. The implications of the differential ability to induce S- and non-S-specific antibody and T cell responses on the durability of protection and protection against virus variants by BNT162b2 and CoronaVac, the 2 most used SARS-CoV-2 vaccines in the world, should be further investigated. Our results support the use of both vaccines in adolescents.