The timing of local SARS-Cov-2 outbreaks and vaccination coverage during the Delta wave in Melbourne

This article presents a longitudinal analysis of COVID-19 infection and vaccination coverage in Melbourne metropolitan local government areas (LGAs) during the 2021 Delta wave.

COVID-19 vaccination and infection data from 12 July to 27 November 2021 were sourced from government websites. Summary statistics and associated 95% confidence intervals (95% CI) were compared by LGA ranked according to socioeconomic status: total "burden" (total infections per thousand), "peak" (highest weekly infection rate), "lag" (interval between peak and 70% double vaccination).

LGAs in the bottom five deciles for social advantage experienced higher infection rates (39.0 per thousand [95% CI: 38.5, 39.5] vs. 14.8 [14.7, 14.9]), and had lower two-dose vaccination coverage (23.8% [23.6, 23.9] vs. 32.7% [32.6, 32.7]) compared with LGAs in the top five deciles. LGAs that achieved 70% coverage two weeks or more after the infection peak experienced nearly twice the total infection burden (27.7 per 1000 [27.3, 28.0] compared with 14.9 [14.7, 15.0]) than LGAs with a shorter lag.

Exposure and transmission risk factors cluster within disadvantaged LGAs. The potential for large local outbreaks is heightened if vaccination uptake trails in these communities.

In a pandemic, decision-makers must prioritise disease control and harm reduction interventions for at-risk LGAs.