Identifying Susceptibility of Children and Adolescents to the Omicron Variant (B.1.1.529): A Bayesian Analysis of the Age-Structured Compartmental Model

Background: The Omicron variant (B.1.1.529) is estimated to be more transmissible than previous strains of SARS-CoV-2 especially among children, potentially resulting in croup which is characteristic disease in children. However, there have been no reports confirming this to date.Methods: We developed an age-structured compartmental model, combining age-specific contact matrix in South Korea and observed distribution of periods between each stage of infection in national epidemiological investigation. A Bayesian inference method was used to estimate the age-specific force of infection and, accordingly, age-specific susceptibility, given web-based epidemic data during the third (pre-Delta), fourth (Delta driven), and fifth (Omicron driven) waves in South Korea. As vaccine uptake increased, individuals who were vaccinated were excluded from the susceptible population in accordance with vaccine effectiveness against the Delta and Omicron variants, respectively.Findings: A significant difference between the age-specific susceptibility to the Omicron and that to the pre-Omicron variants was found in the younger age group. The rise in susceptibility to the Omicron/pre-Delta variant was highest in the 10–15 years age group (5·28 times [95% CI, 4·94–5·60]), and the rise in susceptibility to the Omicron/Delta variant was highest in the 15–19 years age group (3·21 times [95% CI, 3·12–3·31]), whereas in those aged 50 years or more, the susceptibility to the Omicron/pre-Omicron remained stable at approximately two-fold.Interpretation; Even after adjusting for contact pattern, vaccination status, and waning of vaccine effectiveness, the Omicron variant of SARS-CoV-2 tends to propagate more easily among children than the pre-Omicron strains.Funding Information: This work was supported by the National Research Foundation of Korea (NRF) grants funded by the Korea government (MSIT) (No. 2020R1A2C3A01003550) and (No. 2021R1F1A1064473).Declaration of Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.Ethics Approval Statement: All the data used in this study were deidentified and were regarded exempt from institutional review board assessment of the National Cancer Center (NCC2022-0127).