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

Objective

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.

Methods

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).

Results

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.

Conclusions

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

Implications for Public Health

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