Title : Immunogenicity and safety of inactivated SARS-CoV-2 vaccine (CoronaVac) using a two-dose primary protocol in children and adolescents (Immunita-002, Brazil): A phase IV one-year follow-up
Abstract:
The immune response induced by SARS-CoV-2 vaccination in children and adolescents is not yet well defined regarding the intensity and duration of protective immunity in the medium and long term, which may indicate the need for booster doses and support public health decisions. Given this context, the aim of this study was to evaluate the immunogenicity, effectiveness, and reactogenicity of the CoronaVac vaccine in children and adolescents aged 3 to 17 years over a one-year period after the second dose. Participants were recruited from public healthcare centers in Serrana (SP) and Belo Horizonte (MG), Brazil, and underwent physical examinations and clinical interviews (CAAE 55183322.6.0000.5091). Blood samples were collected before vaccination, one month after the first dose, and at 1, 3, 6, and 12 months after the second dose. Follow-up included a virtual platform for monitoring adverse events and COVID-19-related symptoms. Cases were confirmed by RT-qPCR and characterized by genomic sequencing (NGS). The humoral immune response was assessed by ELISA for anti- S and anti-N IgG antibodies, and neutralizing antibodies against the B.1 lineage and Omicron variants (BA.1 and BA.5) were quantified by PRNT and VNT50. The cellular immune response was evaluated by flow cytometry, including the quantification of soluble mediators after in vitro antigenic stimulation. Follow-up of 640 participants demonstrated that CoronaVac significantly induced the production of total IgG antibodies against SARS-CoV-2 S and N proteins, as well as neutralizing antibodies against the B.1 lineage and Omicron subvariants BA.1 and BA.5 in both seronegative and seropositive individuals. In addition, a robust cellular immune response was observed, with a broad release of pro-inflammatory and regulatory soluble mediators in the early post-immunization period. Adverse events occurred in 30% of participants and were mostly mild and transient. During follow-up, 8.75% developed mild COVID-19, predominantly associated with BA.2 and BA.5 subvariants. These findings indicate that CoronaVac induces robust humoral and cellular immune responses against SARS-CoV-2 in children and adolescents over one year of follow-up, providing evidence supporting the safety and immunogenicity of this vaccine. Data from this study supported regulatory decisions by ANVISA to expand the use of CoronaVac in children, reinforcing its role as a pediatric immunization strategy against COVID-19. This publication was supported by the Fundação de Amparo à Pesquisa do Estado de Minas Gerais (Fapemig) - Grant APQ-04991-23 and the Instituto René Rachou/Fiocruz Minas
