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

Abstract

Background 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. Methods 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. Results 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% VE for 2 doses of BNT162b2, and 55.0% VE for 2 doses of CoronaVac in adolescents aged 12–18. Conclusions Our findings support partly preserved VE against infection by variants of concerns for children and adolescents in settings with extremely low levels of prior SARS-CoV-2 circulation.

Superior antibody and membrane protein-specific T cell responses to CoronaVac by intradermal versus intramuscular routes in adolescents

“…However, S IgG avidity and cellular immunogenicity against Omicron were maintained, which can possibly explain the persistently high real-life vaccine effectiveness even when it is known that there is waning of quantitative serum antibody concentrations against VOCs. 5,12 Indeed, several human studies have shown that T cell immunity can persist for years after prior exposure and mitigate disease severity when neutralising antibodies are reduced, and the pre-existing antigen-specific T cells are protective against influenza viral infections, severity of symptoms and viral shedding. [32][33][34][35][36] In addition, vaccine-induced T cell responses against the highly conserved structural SARS-CoV-2 membrane protein confers partial protection from lung pathology in a murine model.…”

“…Additionally, the strict social distancing policies that the HK Government mandated during the COVID-19 period kept infection numbers low so that it was not possible to investigate vaccine efficacy in this cohort during this study period, from April 2021 to August 2022 (see Methods). 1,5,12 On the other hand, this provided the opportunity to determine the intradermal vaccine immunogenicity without the confounding effects of existing immunity acquired from past infections. 1,5,12 Moreover, we were able to estimate actual vaccine efficacies using neutralising antibodies.…”

“…10 However, the real-life effectiveness for CoronaVac in the prevention of hospitalisation for adolescents was lower, at ~90% in Chile and HK, and it is further reduced against infection. 5,11,12 As inactivated vaccines, namely CoronaVac, has been amongst the most widely used COVID-19 vaccines for individuals ³3 years old globally, our group performed a humoral and cellular immunobridging study during the early phase of vaccine availability and found non-inferior immunogenicity for CoronaVac in adolescents compared to adults. 13,14 However, CoronaVac induced lower antibody responses than BNT162b2 in adolescents and performed similarly in adolescents as adults.…”

Estimation of reproduction number of SARS-CoV-2 Omicron variant outbreak in Hong Kong

“…This suggests that a significant amount of secondary transmission may occur prior to the symptomatic disease onset, thus facilitating the epidemic. In the fifth wave of HK, the effective Rt remained persistently high even in a context with relevant fully vaccination coverage [23] (see also the “ false colours” contour plot in Figure 1), probably due to the scarce effectiveness of BNT162b2 and CoronaVac against Omicron VOC, especially in children and adolescents [24] .…”

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“…This suggests that a significant amount of secondary transmission may 6 occur prior to the symptomatic disease onset, thus facilitating the epidemic. In the fifth wave of HK, the effective Rt remained persistently high even in a context with relevant full vaccination coverage [22] (see also the "false colors" contour plot in Figure 1), probably due to the scarce effectiveness of BNT162b2 and CoronaVac against Omicron VOC, especially in children and adolescents [23].…”