A case-control study in Brazil during the Omicron wave of the pandemic reveals a two-dose COVID vaccine effectiveness (VE) of 49.4%, 26.0%, and 7.2% for children, adolescents, and young adults, respectively, but it was higher for certain vaccine types.
A three-dose VE against death was 64.5%. The study is published in JAMA Pediatrics and adds to the literature on the effectiveness of the booster doses of COVID-19 vaccines among children and adolescent recipients.
The test-negative case-control study was conducted between December of 2021 and August of 2022. The vaccines available to participants were BNT162b2 (Pfizer-BioNTech RNA vaccine), ChAdOx1 nCoV-19 (the AstraZeneca-Oxford vaccine), and CoronaVac (Sinovac's inactivated vaccine). A total of 2,080,867 children with a positive test result and 3,706,680 controls were included in the final analysis.
For children and adolescents, BNT162b2 had the highest VE(62.3%; (95% conference interval [CI], 60.7% to 63.9%) and 30.8% (95% CI, 28.9% to 32.6%), respectively. For young adults, ChAdOx1 nCoV-19 achieved the highest VE of 29.5%.
"Among adolescents and adults who received the booster dose, VE against symptomatic infection was similar for all vaccine types,” the authors said.
The booster dose was highly protective, however, against death. A third vaccine dose of any type resulted in a significant increase in VE against death for adolescents (80.8%) and young adults (61.7%).
VE against death was still effective after 2 doses for children and the booster dose for adolescents and young adults.
"Regardless of vaccine schedule, we observed low effectiveness in preventing Omicron infection in young people," the authors said. "However, VE against death was still effective after 2 doses for children and the booster dose for adolescents and young adults."