Add SEIRD model with waning immunity

[ben18785]

@DSeiferth and @hfldai pointed me to the Como package where they allow recovered individuals to become susceptible again. In the meeting, we decided to implement a basic SEIRD model where R -> S at a certain rate. We think this'll result in an endemic equilibrium and (possibly) a number of epidemic waves.

[hfldai]

Here's the example plot showing the effects when including R -> S:

• R -> S, transmission rate = 0.01
• No transmission from R -> S

[ben18785]

Ha! That's really interesting. And, I guess, makes sense in terms of oscillatory behaviour since S -> I (and a reduction in S) then, later, I -> R -> S (leading to an increase).

On Thu, Apr 29, 2021 at 10:38 AM Liangti Dai @.***> wrote:

Here's the example plot showing the effects when including R -> S:

• R -> S, transmission rate = 0.01 [image: SEIaImIsRD_omega-0 01] https://user-images.githubusercontent.com/44946606/116530992-9323d980-a8d6-11eb-90a2-c94dd2fca54a.png
• No transmission from R -> S [image: SEIaImIsRD_omega-0] https://user-images.githubusercontent.com/44946606/116531278-e8f88180-a8d6-11eb-8a93-26faecee5da2.png

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[ben18785]

This is in there via #53