Targeted public health interventions and COVID-19 morbidity among children during the SARS-CoV-2 Delta variant outbreak

Abstract

Background: Since August 2021 in Mongolia, the rapid spread of the SARS-CoV-2 Delta variant among the population coincided with the reopening of all levels of educational institutions, including universities, general education schools, and kindergartens, for in-person learning. Aim: To examine the impact of the measures implemented when school was reopened with in-person learning on COVID-19 morbidity among school children, to assess the overall infection situation in children, and to determine whether any school-based outbreak clusters occurred during the Delta variant surge. Materials and Methods: This study used national data from confirmed COVID-19 cases recorded in the electronic surveillance system between January 1, 2021, and February 28, 2022, including all cases and those among children aged 0-17 years. The 7-day moving average of the proportion of cases among children was calculated, representing the average proportion of pediatric cases during the preceding seven days. Additionally, the study compared the incidence and relative risk (RR) of COVID-19 among children aged 0-17 years at the time of school reopening on September 1, 2021, with those observed during previous outbreaks caused by the SARS-CoV-2 Wuhan, Alpha, and Omicron variants. As vaccination was available only for adolescents aged 12-17 years, the analysis was stratified by three age groups: 0-4, 5-11, and 12-17 years. Results: Throughout the study period, the proportion of COVID-19 cases among children aged 0–17 years nationwide ranged from 0.73% to 5.93% across outbreaks caused by the four SARS-CoV-2 variants (min 0.73%; max 8.57%). The 14-day confirmed case rate per 10,000 population was highest during the Delta (107.57) and Omicron (113.56) variant outbreaks. When comparing age groups, children aged 5–11 years were used as the reference group. During outbreaks, the relative risk for the 12–17-year group was lowest during the wild-type virus wave (RR=0.47) and highest during the Delta wave (RR=0.78). Conclusion: During COVID-19 outbreaks, the proportion of pediatric cases (0-17 years) among total cases ranged from 0.73% to 5.93%, consistent with findings from studies conducted in other countries. Overall, infection rates were higher among the 0-4 and 12-17 age groups, with the highest rates among 0-4-year-olds during the Delta variant outbreak. No clustered outbreaks involving six or more cases were reported in school settings. Future studies should focus on assessing the transmission dynamics of respiratory infections among children in both household and school settings, especially during influenza and influenza-like illness outbreaks, to generate evidence for preventive measures against respiratory pathogen transmission.