RESUMO
The SARS-CoV-2 Omicron variant has challenged the control of the COVID-19 pandemic even in highly vaccinated countries. While a second booster of mRNA vaccines improved the immunity against SARS-CoV-2, the humoral and cellular responses induced by a second booster of an inactivated SARS-CoV-2 vaccine have not been studied. In the context of a phase 3 clinical study, we report that a second booster of CoronaVac(R) increased the neutralizing response against the ancestral virus yet showed poor neutralization against the Omicron variant. Additionally, isolated PBMCs displayed equivalent activation of specific CD4+ T cells and IFN-{gamma} production when stimulated with a mega-pool of peptides derived from the spike protein of the ancestral virus or the Omicron variant. In conclusion, a second booster dose of CoronaVac(R) does not improve the neutralizing response against the Omicron variant compared with the first booster dose, yet it helps maintaining a robust spike-specific CD4+ T cell response.
RESUMO
BackgroundMultiple vaccines against SARS-CoV-2 have been evaluated in clinical trials, but very few include the pediatric population. The inactivated vaccine CoronaVac(R) has shown to be safe and immunogenic in a phase 1/2 clinical trial in a pediatric cohort in China. This study is an interim safety and immunogenicity report of a phase 3 clinical trial for CoronaVac(R) in healthy children and adolescents in Chile. MethodsParticipants aged 3 to 17 years old received two doses of CoronaVac(R) in a four-week interval. Local and systemic adverse reactions were registered in 699 participants that received the first dose and 381 that received the second dose until December 31st, 2021. Whole blood samples were collected from 148 participants for humoral and cellular immunity analyses. ResultsThe primary adverse reaction reported after the first and second dose was pain at the injection site. The adverse reactions observed were primarily mild and local, and no severe adverse events were reported. Four weeks after the second dose, a significant increase in the levels of total and neutralizing antibodies was observed. Increased activation of specific CD4+ T cells was also observed four weeks after the second dose. Although antibodies induced by vaccination neutralize variants Delta and Omicron, titers were lower than the D614G variant. Importantly, comparable T cell responses were detected against these variants of concern. ConclusionsCoronaVac(R) is safe and immunogenic in subjects aged 3-17 years old and is thus likely to confer protection against infection caused by SARS-CoV-2 variants in this target population.
