Journal of The Royal Society Interface· 2026Q1
Quantifying the direct and indirect impact of COVID-19 vaccination: evidence from Victoria, Australia
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- Q1SCImago
- 2026year
Short summary
A new method to quantify indirect COVID-19 vaccination benefits reveals that during Victoria's Delta outbreak, indirect protection averted 315,000 infections, 33,400 hospitalizations, and 4,900 deaths, accounting for half of averted infections and around a quarter of averted hospitalizations and deaths.
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Key points
- A new method was developed to quantify indirect population-level benefits of vaccination.
- During Victoria's Delta outbreak, vaccination averted an estimated 315,000 infections, 33,400 hospitalizations, and 4,900 deaths.
- Indirect protection accounted for half of averted infections and approximately one-quarter of averted hospitalizations and deaths.
- Homogeneous vaccination across local government areas could have reduced outcomes by an additional 25%.
AI-generated from the title and abstract; the full text is not read.
Abstract
Vaccines not only directly protect vaccinated individuals but also contribute to protecting the entire population via indirect herd-immunity benefits. However, researchers have long struggled to quantify these indirect effects at the population level, hindering the assessment of vaccination programme 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, reveals strong indirect effects during the Delta outbreak (September-November 2021). By modelling a non-vaccination counterfactual, we conservatively estimate 315 000 infections were averted (95% Bayesian credible interval (BCI): 231k-406k), as well as 33 400 hospitalizations (95% BCI: 22k-46k), and 4900 deaths (95% BCI: 2.8k-7.2k). 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 local government areas could have reduced outcomes by approximately 25%.
The authors' abstract, as published at the source. Journal of The Royal Society Interface, 2026 · DOI ↗
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Field: Health
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