Quantifying the direct and indirect impact of COVID-19 vaccination: evidence from Victoria, Australia
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arXiv
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| Format: | Preprint |
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2025
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| author | Lin, Lixin Demirhan, Haydar Eizenberg, Peter Trauer, James M. Stone, Lewi |
| author_facet | Lin, Lixin Demirhan, Haydar Eizenberg, Peter Trauer, James M. Stone, Lewi |
| contents | Vaccines not only directly protect vaccinated individuals but also contribute to protect the entire population via indirect herd-immunity benefits. However, researchers have long struggled to quantify these indirect effects at the population level, hindering assessment of vaccination program effectiveness. We developed a new method to estimate these effects, thereby markedly improving measures of the number of infections, hospitalizations, and deaths averted by vaccination. Our population-based analysis of 6,440,000 residents of Victoria, Australia reveal strong indirect effects during the Delta outbreak (September-November 2021). By modelling a non-vaccination counterfactual, we conservatively estimate 316,000 infections were averted (95\% BCI: 232k-406k), as well as 33,500 hospitalizations (95\% BCI: 22.2k-46.2k), and 4,900 deaths (95\% BCI: 2.9k-7.3k). These are 4.0, 7.5, and 8.0 times higher, respectively, than observed. Half of the averted infections and around one-quarter of hospitalizations and deaths were attributable to indirect protection. Homogeneous vaccination across LGAs could have reduced outcomes by approximately 25\%. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_08763 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Quantifying the direct and indirect impact of COVID-19 vaccination: evidence from Victoria, Australia Lin, Lixin Demirhan, Haydar Eizenberg, Peter Trauer, James M. Stone, Lewi Populations and Evolution Quantitative Methods Vaccines not only directly protect vaccinated individuals but also contribute to protect the entire population via indirect herd-immunity benefits. However, researchers have long struggled to quantify these indirect effects at the population level, hindering assessment of vaccination program effectiveness. We developed a new method to estimate these effects, thereby markedly improving measures of the number of infections, hospitalizations, and deaths averted by vaccination. Our population-based analysis of 6,440,000 residents of Victoria, Australia reveal strong indirect effects during the Delta outbreak (September-November 2021). By modelling a non-vaccination counterfactual, we conservatively estimate 316,000 infections were averted (95\% BCI: 232k-406k), as well as 33,500 hospitalizations (95\% BCI: 22.2k-46.2k), and 4,900 deaths (95\% BCI: 2.9k-7.3k). These are 4.0, 7.5, and 8.0 times higher, respectively, than observed. Half of the averted infections and around one-quarter of hospitalizations and deaths were attributable to indirect protection. Homogeneous vaccination across LGAs could have reduced outcomes by approximately 25\%. |
| title | Quantifying the direct and indirect impact of COVID-19 vaccination: evidence from Victoria, Australia |
| topic | Populations and Evolution Quantitative Methods |
| url | https://arxiv.org/abs/2508.08763 |