Vaccine effectiveness of CoronaVac against COVID-19 among children in Brazil during the Omicron period

Although severe COVID-19 in children is rare, they may develop multisystem inflammatory syndrome, long-COVID and downstream effects of COVID-19, including social isolation and disruption of education. Data on the effectiveness of the CoronaVac vaccine is scarce during the Omicron period. In Brazil, children between 6 to 11 years are eligible to receive the CoronaVac vaccine. We conducted a test-negative design to estimate vaccine effectiveness against symptomatic infection and hospitalization among children aged 6 to 11 years. This study included data from 197,958 residents from January 21, 2022, to April 15, 2022, during the Omicron dominant period in Brazil among children aged 6 to 11 years. The estimated vaccine effectiveness for symptomatic infection was 39.8% (95% CI 33.7–45.4) at ≥14 days post-second dose. For hospitalization vaccine effectiveness was 59.2% (95% CI 11.3–84.5) at ≥14 days. Two doses of CoronaVac in children during the Omicron period showed low levels of protection against symptomatic infection, and modest levels against severe illness.

Pilar T. V. Florentino, Flávia J. O. Alves, Thiago Cerqueira-Silva, Vinicius de Araújo Oliveira, Juarey B. S. Júnior, Adelson G. Jantsch, Gerson O. Penna, Viviane Boaventura, Guilherme L. Werneck, Laura C. Rodrigues, Neil Pearce, Manoel Barral-Netto, Maurício L. Barreto, Enny S. Paixão