Age and household transmission of SARS-CoV-2 in the Bangkok metropolitan region, Thailand, 2022-2024

ABSTRACT
We examined age-related effects on SARS-CoV-2 household transmission in 60 households (266 participants), all enrolled in the Bangkok metropolitan region, Thailand, between November 2022 and August 2024. All index cases were COVID-19 patients under 18 years of age, identified at the Pediatrics Outpatient Department, Ramathibodi Hospital, Bangkok. Each household was followed for up to four weeks, and viral genomes were sequenced to determine lineages and cluster structures.
Households with child primary case(s) showed significantly lower proportions ofCOVID-19 cases at both enrolment and study endpoint compared with Households with adult primary case(s), and children were at greater risk of infection where the first case was an adult (or an adult and child concurrently) than inchild-first households. Viral genomes were successfully recovered from 128 of170 cases (75.3%), all belonging to Omicron subvariants: BA.2.75 (n = 30),BA.2.86 (n = 34), BA.5 (n = 5), XBB (n = 57), and XBL (n = 2). Phylogenetic analysis revealed multiple introductions and epidemiological linkages across households, and tip-dating analysis suggested that, of the identified 69sequence clusters, of which 60 (87.0%) persisted less than 14 days and 67 (97.1%)less than 21 days. Symptom severity was not associated with age, household type, or viral lineage, but was correlated with RT-PCR Ct values of the orf1abgene. Children overall exhibited a higher risk of infection than adults, with infection rates differing among household types, but not viral lineages.