# Estimating the impact of decreasing vaccination response times for outbreaks of vaccine-preventable diseases in low- and middle-income countries

## TL;DR

The study shows that faster vaccination responses during outbreaks in low- and middle-income countries can significantly reduce disease cases and outbreak risks.

## Contribution

The novelty lies in using agent-based models to estimate the impact of faster outbreak response immunization across four diseases in low- and middle-income countries.

## Key findings

- A 15-day ORI response could avert up to 80% of cholera cases compared to a 105-day historical response.
- Faster ORI responses could reduce meningococcal meningitis cases by 35% relative to a 75-day historical response.
- Even a slow vaccination response is beneficial compared to no response at all in reducing outbreak risks.

## Abstract

The 7–1–7 targets are gaining traction as measurable targets for assessing a country’s readiness to detect and respond to outbreaks of infectious diseases. The targets are outbreak detection within 7 days of emergence, notification to health authorities within 1 day, and key early response actions commenced within another 7 days. For outbreaks of measles, cholera, yellow fever, and meningococcal meningitis, we estimated the impact of initiating outbreak response immunisation (ORI) within 15 days of outbreak emergence, relative to the mean ORI response time for each disease in low- and middle-income countries (LMICs) since 2000. Initiating ORI within 15 days of outbreak emergence aligns with the 7–1–7 targets and supports outbreak containment.

Using agent-based models for four diseases, a status quo and series of ‘Faster response’ scenarios were compared for simulated outbreaks of each disease, with a 15-day ORI response time as the minimum. The Starsim modelling framework was used to build the models to provide a single common software and analysis architecture for all models while having the flexibility to account for very different modes of transmission across the diseases being modelled. The models were calibrated to epidemiological and programmatic response data for 51 measles, 40 cholera, 24 meningococcal meningitis, and 88 yellow fever outbreaks in LMICs.

In a synthetic model population, a 15-day ORI response could avert: 80% of cases from cholera outbreaks relative to a historical response time of 105 days, 35% of cases from meningococcal meningitis outbreaks relative to a historical response time of 75 days, 0–35% of cases from yellow fever outbreaks relative to a historical response time of 105 days (depending on routine vaccine coverage and environmental suitability), and 0–55% of cases from measles outbreaks relative to a historical response time of 120 days (depending on routine vaccine coverage).

Improvements made to ORI response time could reduce disease burden and decrease the risk of large outbreaks of vaccine-preventable diseases in LMICs. Efforts to improve ORI timeliness should be prioritised to higher risk settings, and it was clear that even a slow vaccination response was beneficial relative to no response at all.

The online version contains supplementary material available at 10.1186/s44263-025-00239-6.