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Time-optimal control strategies in SIR epidemic models
Luca Bolzoni1, Elena Bonacini2, Cinzia Soresina3
1Risk Analysis Unit, Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna, Via dei Mercati 13, Parma 43126, Italy.
Optimal control strategies for SIR epidemic models reveal that delaying interventions like vaccination or isolation, then applying them maximally, is often time-optimal. This contrasts with minimizing overall disease burden, highlighting trade-offs between speed and impact.
Area of Science:
- Epidemiology
- Mathematical Biology
- Control Theory
Background:
- Susceptible-Infected-Recovered (SIR) models are fundamental in understanding epidemic dynamics.
- Optimal control theory seeks to minimize disease spread and duration using interventions.
- Previous studies often focused on minimizing total infectious burden, not necessarily outbreak duration.
Purpose of the Study:
- To investigate time-optimal control strategies for SIR epidemic models.
- To analyze the effectiveness of different control policies: vaccination, isolation, culling, and transmission reduction.
- To determine if minimizing epidemic duration conflicts with minimizing total infectious burden.
Main Methods:
- Application of Pontryagin's Minimum Principle (PMP) to unconstrained SIR models.
- Analysis of bang-bang control strategies with at most one switch.
- Numerical simulations to explore complex scenarios and unexpected outcomes.
Main Results:
- For time-optimal control, bang-bang strategies with a single switch are optimal across various policies.
- The optimal strategy involves delaying control application and then implementing it at maximum rate.
- This contrasts with strategies for minimizing total infectious burden, which favor continuous maximal control.
- Numerical simulations revealed delayed optimal control even with a reproduction number below one, and switching post-peak infection.
Conclusions:
- Minimizing epidemic duration and total infectious burden may be conflicting objectives in SIR models.
- Delayed, maximal control application is a key finding for time-optimal epidemic management.
- Results have significant implications for livestock disease control, where minimizing outbreak duration is critical due to economic restrictions.
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