W172 - Immune Responses During COVID-19 Breakthrough Cases in Vaccinated Children and Adolescents

Katia Abarca – Pontificia Universidad Católica de Chile; Mónica Acevedo – Universidad de Chile; Susan M Bueno – Pontificia Universidad Católica de Chile; Benjamín Diethelm-Varela – Millennium Institute on Immunology and Immunotherapy, Santiago, Chile. Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile. – Pontificia Universidad Católica de Chile; Rodrigo Fasce – Instituto de Salud Publica de Chile; Jorge Fernandez – Instituto de Salud Pública de Chile; Pablo A Gonzalez – Pontificia Universidad Católica de Chile; Alba Grifoni – Center for Vaccine Innovation, La Jolla Institute for Immunology (LJI); Alexis M Kalergis – Pontificia Universidad Católica de Chile; Nicole Le Corre – Pontificia Universidad Católica de Chile; Felipe Melo-González – Departamento de Ciencias Biológicas, Facultad de Ciencias de la Vida, Universidad Andrés Bello, Santiago 8370146, Chile. – Universidad Andrés Bello; Constanza Mendez – PhD Student, 1. Millennium Institute on Immunology and Immunotherapy, Santiago, Chile. 2. Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile., Pontificia Universidad Católica de Chile; Xing Meng – SINOVAC; Judith Mora – Instituto de Salud Pública de Chile; Cecilia Perret – Pontificia Universidad Católica de Chile; Eugenio Ramirez – Instituto de Salud Pública de Chile; Alessandro Sette – Center for Vaccine Innovation, La Jolla Institute for Immunology (LJI), La Jolla, CA 92037; Jorge Soto – Universidad Andrés Bello; Ricardo Soto – Universidad de Chile; Fernando Valiente-Echeverría – Universidad de Chile; Yaneisi Vazquez – Pontificia Universidad Católica de Chile; Daniela Weiskopf – Center for Vaccine Innovation, La Jolla Institute for Immunology (LJI), La Jolla, CA 92037; Quianqian Xin – SINOVAC

Abstract Text: Vaccine effectiveness against SARS-CoV-2 infection has been somewhat limited due to the widespread dissemination of the Omicron variant and its subvariants , and the immune response dynamics of the naturally infected with the virus.

Methods: Twelve subjects between 3-17 yo, vaccinated with two doses of CoronaVac®, were followed and diagnosed as breakthrough cases starting 14 days after receiving the second dose. Total IgGs against different SARS-CoV-2 proteins and neutralizing capacity of these antibodies were measured in plasma. The activation of CD4+ and CD8+ T cells was evaluated in peripheral blood mononuclear cells stimulated with peptides derived from the proteins from the wild-type (WT) virus and Omicron subvariants by flow cytometry, as well as different cytokines secretion by Luminex.

Results: 2 to 8 weeks post-infection, as compared to 4 weeks after 2nd dose of vaccine, there was a 146-fold increase in neutralizing antibody titers against Omicron and a 39-fold increase against WT SARS-CoV-2. Subjects showed an increase in total IgG levels against the S1, N, M, and NSP8 proteins of the WT virus. Activation of CD4+ T cells showed a significant in response to BA.2 subvariant (p < 0.001). Finally, the secretion of IL-2 and IFN-ɣ cytokines showed an increase trend after infection.

Conclusion: SARS-CoV-2 infection in pediatric population vaccinated with an inactivated SARS-CoV-2 increased neutralizing antibodies against Omicron and increased specific IgG antibodies for different SARS-CoV-2 proteins. Also, CD4+ T cell activation was increased, suggesting a maintained conserved cellular response against the Omicron subvariants, whereas Th1-type cytokine secretion tended to be decreased.