W153 - Protective Humoral and Cellular Immunity Induced by an Inactivated sars-cov-2 Vaccine in Phase 3 Clinical Trials

Nicolás M S Gálvez; Gaspar A Pacheco; Bárbara M Schultz; Felipe Melo-González; Jorge A Soto; Luisa F Duarte; Liliana A González; Daniela Rivera-Pérez; Mariana Ríos; Roslye V Berrios; Yaneisi Vázquez; Daniela Moreno-Tapia; Omar P Vallejos; Catalina A andrade; Guillermo Hoppe-Elsholz; Carolina Iturriaga; Marcela Urzua; María S Navarrete; Álvaro Rojas; Rodrigo Fasce; Jorge Fernández; Judith Mora; Eugenio Ramírez; Aracelly Gaete-Argel; Mónica L Acevedo; Fernando Valiente-Echeverría; Ricardo Soto-Rifo; Daniela Weiskopf; Alba Grifoni; Alessandro Sette; Gang Zeng; Weining Meng; José V González-Aramundiz; David Goldblatt; Contanza mendez; Pablo A González; Katia Abarca; susan M Bueno

Abstract Text: An inactivated SARS-CoV-2 vaccine was approved for emergency use with significant efficacy and immunogenicity reported in several trials. In a randomized, multicenter, and controlled phase 3 trial in healthy adults, volunteers received two doses of the inactivated SARS-CoV-2 vaccine separated by 2 (0-14 schedule) or 4 weeks (0-28 schedule), with boosters given at 6 and 12 months. Humoral and cellular immune responses were evaluated by measuring the neutralizing antibodies and T cell activation. Both schedules exhibited robust neutralizing capacities, but the 0-28 schedule showed better responses. No differences were found in the concentration of antibodies against the virus and different variants of concern between schedules. PBMC stimulation with peptide mega pools induced the secretion of IFN-γ and the expression of activation-induced markers in CD4+ T cells, and significant correlations were observed. Although a 2.5-fold increase in ancestral SARS-CoV-2 neutralization was observed after the second booster when compared with prior its administration a reduced neutralization against the Omicron variant was detected. Activation of CD4+ T lymphocytes remained stable after the second booster and, importantly, equivalent activation of CD4+ T lymphocytes against the Omicron variant and the ancestral SARS-CoV-2 were found. Although the neutralizing response against the Omicron variant after the second booster was slightly increased, these levels were lower than those observed for the ancestral SARS-CoV-2. In contrast, robust CD4+ T cell responses may confer protection against the Omicron variant. Immunization with this inactivated SARS-CoV-2 vaccine promotes robust cellular and humoral immune responses, with a better profile in the 0-28 schedule.