Observation model:E[yt]=N⋅pobs⋅[I2(t)+R(t)−(I2(t−1)+R(t−1))]xt=[S(t),E1(t),E2(t),I1(t),I2(t),R(t),βi(t),σ,γ,τ]ℒ(yt∣xt)∼NegBin(E[yt],k)