Public health interventions successfully mitigated multiple incursions of SARS-CoV-2 Delta variant in the Australian Capital Territory

Abstract

The Australian Capital Territory rapidly responded to an incursion of the SARS-CoV-2 Delta (B.1.617.2) variant on 12 August 2021 with several public health interventions, including a territory-wide lockdown and genomic sequencing. Prior to this date, SARS-CoV-2 had been eliminated locally since July 7, 2020. Sequencing of >75% of cases identified at least 13 independent incursions with onwards spread in the community during the study period, between 12 August and 11 November 2021. Two incursions resulted in the majority of community transmission during this period, with persistent transmission in vulnerable sections of the community. Ultimately, both major incursions were successfully mitigated through public health interventions, including COVID-19 vaccines. In this study we explore the demographic factors that contributed to the spread of these incursions. The high rates of SARS-CoV-2 sequencing in the Australian Capital Territory and the relatively small population size facilitated detailed investigations of the patterns of virus transmission. Genomic sequencing was critical to disentangling complex transmission chains to target interventions appropriately.