Linmar Rodríguez‐Guilarte, Constanza Méndez, Antonia Reyes, Mariana Ríos, Francisca Román, Daniela Moreno‐Tapia, Alex Cabrera, Daniela Rivera, Cristián Gutiérrez-Vera, Pablo A. Palacios, Andrea Schilling, Sofía Aljaro, Francisca Bascur, Álvaro Rojas, Constanza Del Río, Patricio Astudillo, Carlos M. Pérez, Loreto Perez, Maite Oyonarte, Patricia E. Fernández Vásquez, Rosa Feijoo, Daniel Beltrán Campos, Carlos Tovar De Sousa, Andrea Castejón, Silvana Grandón, Marcela Villarroel, P. Jara, Loreto Twele, Marisa Domínguez, José Vicente González-Aramúndiz, María Javiera Álvarez-Figueroa, Wanqi Yang, Qianqian Xin, Leandro J. Carreño, Mario Calvo, Susan M. Bueno, Hernán F. Peñaloza, Pablo A. González, Alexis M. Kalergis
Annual vaccination is an effective strategy for preventing severe disease caused by seasonal influenza. Quadrivalent influenza vaccines (QIVs) protect against two strains of influenza A and two strains of influenza B, thereby enhancing the host antiviral neutralizing antibody response and inducing CD4+ and CD8+ T cell responses. Here, we report findings from a randomized, double-blind, active-controlled phase 3 clinical trial (NCT05431725) that includes 334 healthy adults aged 18–64 years and evaluates the humoral and cellular antiviral immune responses induced by two inactivated QIVs, Sinovac-QIV and Vaxigrip-Tetra™. The primary endpoint of the study is the specific antibody responses measured by hemagglutination inhibition (HAI) assays 28 days post-vaccination, while the secondary endpoint is virus-specific T cell responses. Both QIVs elicit significant increases in antibody titers 28 days after vaccination; Sinovac-QIV induces 9–10-fold increases in geometric mean titers, while Vaxigrip-Tetra™ elicits 7–8-fold increases (p < 0.05). Cellular immune responses using ELISPOT and supervised and unsupervised flow cytometry analyses show that both vaccines modulate the frequency of hemagglutinin-specific CD4+ and CD8+ T cell subsets, inducing distinct T cell response profiles. Although cellular analyses are evaluated in a subgroup of the cohort, the data indicate that both QIVs induce robust humoral and cellular immunity in adults, providing mechanistic insights into vaccine-induced protection. The authors report a trial subset analysis of the immune responses induced by two inactivated quadrivalent influenza vaccines (QIVs): Sinovac QIV and Vaxigrip-Tetra™. Both vaccines elicit robust humoral responses and distinct T cell profiles.