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

Background

Globally, infectious disease outbreaks cause a major health and economic burden. For infectious diseases which have existing vaccines, reactive vaccination programs during an outbreak are a powerful tool for reducing disease transmission — preventing infections and deaths. However, despite awareness, monitoring, and accessible stockpiles of vaccines, it can take months for vaccines to be delivered once outbreaks are detected in low-resource settings.

The 7-1-7 targets are gaining traction as measurable targets for assessing a country’s outbreak readiness. The targets are outbreak detection within seven days of emergence; notification to health authorities within one day; and key early response actions commenced within another seven days. For outbreaks of measles, cholera, yellow fever, and meningococcal meningitis, we aim to estimate 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.

While only one component of outbreak response, initiating ORI within 15-days of outbreak emergence aligns with 7-1-7 targets and supports outbreak containment.

Methods

Using calibrated 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.

Results

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).

Conclusions

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.