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=St−βSt(IR,t+ID,t)Nt+ωRt Et+1=Et+βSt(IR,t+ID,t)Nt−δEt+ϵ IR,t+1=IR,t+δ(1−μ)Et−γRIR,t+ϵ ID,t+1=ID,t+δμEt−γDID,t+ϵ Rt+1=Rt+γRIR,t−ωRt Dt+1=Dt+γDID,t