Stochastic SEIRD model

The model is SEIRD model, where infected individuals can survive or die at different rates, with waning immunity. The full model specification is:

  • S: susceptibles
  • E: exposed, i.e. infected but not yet contagious
  • IR: infectious who will survive
  • ID: infectious who will die
  • R: recovered
  • D: dead

There are no birth of natural death processes in this model. Parameters are:

  • β: rate of infection
  • δ: rate at which symptoms appear (i.e inverse of mean incubation period)
  • γR: recovery rate
  • γD: death rate
  • μ: case fatality ratio (proportion of cases who die)
  • ϵ: import rate of infected individuals (applies to E and I)
  • ω: rate waning immunity

The model will be written as:

St+1=StβSt(IR,t+ID,t)Nt+ωRt Et+1=Et+βSt(IR,t+ID,t)NtδEt+ϵ IR,t+1=IR,t+δ(1μ)EtγRIR,t+ϵ ID,t+1=ID,t+δμEtγDID,t+ϵ Rt+1=Rt+γRIR,tωRt Dt+1=Dt+γDID,t