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.

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.