Immunogenicity and safety of inactivated SARS-CoV-2 vaccine (CoronaVac) using two-dose primary protocol in children and adolescents (Immunita-002, Brazil): A phase IV six-month follow up
Authors: Corsini Camila Amormino , Martins Priscila Fernanda da Silva , Filgueiras Priscilla Soares , Lourenço Adelina Júnia , Lima Ana Esther de Souza , Gomes Sarah Vieira Contin , Jeremias Wander de Jesus , Alves Pedro Augusto , Fernandes Gabriel da Rocha , Castro Luciana Lisboa Mota e , Teixeira-Carvalho Andrea , Campi-Azevedo Ana Carolina , Curimbaba Caroline De Almeida Leitao , Lorencini Daniela Aparecida , Junior Eolo Morandi , Silva Victor Mattos da , Cervi Maria Célia , Borges Marcos de Carvalho , Nogueira Maurício Lacerda , Campos Guilherme Rodrigues Fernandes , Correa Paulo Roberto Lopes , Carvalho Taciana Malheiros Lima , Reis Jordana Grazziela Alves Coelho dos , Reis Erik Vinicius de Sousa , Castilho Leda dos Reis , de Lima Poliana Remundini , Nascimento João Paulo Resende do , de Oliveira Jaquelline Germano , Martins-Filho Olindo Assis , Grenfell Rafaella Fortini Queiroz e , Team Immunita 
Published: February 2024

Introduction:
Vaccines are essential for the prevention and control of several diseases, indeed, monitoring the immune response generated by vaccines is crucial. The immune response generated by vaccination against SARS-CoV-2 in children and adolescents is not well defined regarding to the intensity and medium to long-term duration of a protective immune response, which may point out the need of booster doses and might support the decisions in public health.
Objective
The study aims to evaluate the immunogenicity and safety of inactivated SARS-CoV-2 vaccine (CoronaVac) in a two-dose primary protocol in children and adolescent aging from 3 to 17 years old in Brazil.
Methods
Participants were invited to participate in the research at two public healthcare centers located in Serrana (São Paulo) and Belo Horizonte (Minas Gerais), Brazil. Participants underwent medical interviews to gather their medical history, including COVID-19 history and medical records. Physical exams were conducted, including weight, blood pressure, temperature, and pulse rate measurements. Blood samples were obtained from the participants before vaccination, 1 month after the first dose, and 1, 3, and 6 months after the second dose and were followed by a virtual platform for monitoring post-vaccination reactions and symptoms of COVID-19. SARS-CoV-2 genome from Swab samples of COVID-19 positive individuals were sequenced by NGS. Total antibodies were measured by ELISA and neutralizing antibodies to B.1 lineage and Omicron variant (BA.1) quantified by PRNT and VNT. The cellular immune response was evaluated by flow cytometry by the quantification of systemic soluble immune mediators.
Results
The follow-up of 640 participants showed that the CoronaVac vaccine (Sinovac/Butantan Institute) was able to significantly induce the production of total IgG antibodies to SARS-CoV-2 and the production of neutralizing antibodies to B.1 lineage and Omicron variant. In addition, a robust cellular immune response was observed with wide release of pro-inflammatory and regulatory mediators in the early post-immunization moments. Adverse events recorded so far have been mild and transient except for seven serious adverse events reported on VigiMed.
Conclusions
The results indicate a robust and sustained immune response induced by the CoronaVac vaccine in children and adolescents up to six months, providing evidences to support the safety and immunogenicity of this effective immunizer.