COVID-19 vaccine uptake among children and adolescents in Norway: A comprehensive registry-based cohort study of over 800,000 individuals

•In Norway, 12–17-year-olds had greater COVID-19 vaccine uptake than younger children of age 5–11 years.•About one every eight children aged 5–11 years with high risk for severe COVID-19 was unvaccinated.•Parental COVID-19 vaccination status, especially in the mother, was major determinant of COVID-19 vaccine uptake in children and adolescents.•Prior SARS-CoV-2 infection, being born premature and having moderate or high risk of severe COVID-19 were important determinants of vaccine uptake. Factors related with COVID-19 vaccine uptake in children and adolescents in Norway remain unclear, despite this being useful knowledge for future pandemic preparedness. This study aimed to comprehensively examine individual and familial factors associated with vaccine uptake in children and adolescents in Norway. We utilized nationwide registry-data from various health registries and Statistics Norway, encompassing all children and adolescents living in Norway during the pandemic, until 31-Dec-2022. Vaccine uptake is defined as receiving at least one dose of COVID-19 vaccine. We employed a forward stepwise logistic regression model and a random forest machine-learning algorithm to explore the relationship between vaccine uptake and socio-cultural, demographic, and health-related factors. We included 423,548 5–11-year-olds, 269,830 12–15-year-olds, and 120,854 16–17-year-olds. Vaccine uptake in these three groups was respectively 2.6 %, 73.3 %, and 87.3 %. Factors associated with vaccine uptake varied by age group. In youngest children, immigrant background (Odds-ratio (OR) = 1.58, 95 % confidence interval (CI) (1.14–2.19)), born extremely preterm (OR = 2.38, 95 % CI (1.60–3.54)), having risk of severe COVID-19 (OR = 5.40, 95 % CI (4.69–6.23) and maternal COVID-19 vaccination (OR = 6.34, 95 % CI (5.35–7.53)) were positively associated with vaccine uptake. The latter two factors were also strongly, positively associated with vaccine uptake in 12–15-year-olds, while previous SARS-CoV-2 infection was negatively associated (OR = 0.12, 95 % CI (0.11–0.14). Similar findings were observed in 16–17-year-olds. COVID-19 vaccine uptake differed markedly by age group, and major associated factors included socio-demographics and parental COVID-19 vaccination status, prior SARS-CoV-2 infection, but also being born premature and having moderate or high risk of severe COVID-19.