Abstract
This case-control study spanned from July 2022 to September 2023, focusing on the pre-Omicron COVID-19 mRNA vaccine effectiveness against the Omicron variant in children without prior SARS-CoV-2 exposure. We reported that pre-Omicron COVID-19 mRNA vaccines significantly reduced Omicron-induced hospitalizations in infection-naïve Taiwanese children. Our study also highlighted the socioeconomic factors influencing COVID-19 vulnerability among the children population.