Investigations into a trigger-based approach for initiating emergency vaccination to augment stamping-out of foot-and-mouth disease in New Zealand: a simulation study
Creators: name: Sanson, RL
name: Yu, ZD
name: Rawdon, TG
name: van Andel, M
Publisher: name: Taylor & Francis
Year: 2021
Subjects: subject: Medicine
subject: Biotechnology
subject: Sociology
subject: FOS: Sociology
subject: 69999 Biological Sciences not elsewhere classified
subject: FOS: Biological sciences
subject: 19999 Mathematical Sciences not elsewhere classified
subject: FOS: Mathematics
subject: Cancer
subject: 110309 Infectious Diseases
subject: FOS: Health sciences
subject: Computational Biology

description: : To investigate the benefits of an adaptive management approach to the deployment of emergency vaccination as an additional measure to stamping-out (SO) during simulated outbreaks of foot-and-mouth disease (FMD) in New Zealand. A simulation modelling (n=6000 simulations) approach was used. The study population comprised all known farms in New Zealand with FMD-susceptible livestock. Each simulation started with infection seeded into a single randomly selected farm in the upper North Island. Transmission mechanisms included direct and indirect contacts, local and airborne spread. Each outbreak was randomly assigned to one of four control strategies, comprising SO only; trigger-based vaccination (TRV) where SO was augmented with vaccination if an early decision indicator trigger operating between Days 11–35 of the response indicated a large outbreak was developing; SO plus vaccination started randomly on Days 11–35 of the response (VACr); and SO plus vaccination with a fixed start on Day 21 of the response (VACf). A range of other parameters such as the number of personnel resources available were also varied randomly. Generalised additive models (GAM) and tree-based regression analyses were used to evaluate variables associated with the number of detected infected premises (IP) and epidemic duration. The mean number of IP was 29 (median 9, min 1, max 757), while epidemics lasted on average 26.9 (median 18, min 1, max 220) days. These excluded 303 that were extreme, outbreaks larger than the UK 2001 FMD epidemic (2,030 cases). Univariable analysis of the pooled vaccination results <i>vs</i>. SO, showed that vaccination significantly reduced the number of IP (p&lt;0.001) and outbreak duration (p&lt;0.001). GAM of large outbreaks revealed that only the TRV strategy was significantly protective compared to SO alone, reducing the odds of a large outbreak by 22% (OR=0.78; 95% CI=0.63–0.96). Farm class of the primary case was associated with the odds of a large outbreak, with dairy support farms associated with a 53% increase in odds of a large outbreak relative to dairy farms (OR=1.53; 95% CI=1.1–2.12). For each additional farm that a surveillance veterinarian could visit per day, the odds of a large outbreak reduced by 10% (OR=0.9, 95% CI=0.86–0.95). The number of veterinarians exhibited a non-linear association with large outbreaks, with low veterinarian numbers increasing the odds of a large outbreak, but once veterinarian numbers approached 200, the odds of a large outbreak reduced. Time to first detection also had a non-linear relationship with large outbreaks, with detections &lt;13 days being protective and longer detection times increasing the odds of a large outbreak. GAM of long outbreaks showed similar findings, except that all three vaccination strategies significantly reduced duration. Overall, the TRV strategy resulted in the smallest and shortest epidemics. An adaptive management approach that deployed vaccination in response to a trigger when a large outbreak was developing outperformed SO and reduced the odds of a large or long outbreak more than the other two non-trigger based vaccination strategies, although the differences between the three vaccination strategies were statistically small. This study provides highly relevant insights into the dynamics of disease establishment and spread that will guide New Zealand’s readiness for responding to highly infectious disease incursions such as FMD.