Lesson 6 of 10
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SEIR & SEIRW models for Hepatitis E Virus (HEV) Outbreaks: A Case Study


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Mackshon

Am still failing to understand the beta = 120, how can we derive this?

Mackshon

Hi. When modelling the HEV outbreak in the IDP camp. (41:52 mins into the video)

Screenshot-2026-05-18-074130
Alaric

I am having some trouble understanding sigma in the case study. At 42:00 in the video it is given as 52/5 corresponding to 1/latent period. This does not make sense if symptomatic incidence is p * sigma * E because if p =1/7 then p * sigma is greater than 1 indicating higher symptomatic cases than exposed cases.
Then at 54:00 in the video, sigma is given as 0.2 which makes more sense to me than 52/5, but I am not sure where 0.2 came from.

Could someone help with understanding the two different values for sigma?

Bruna

I have the same question 🙂 she said sigma was 52/5 and then that sigma was 0.2 in the R model. I think 0.2 is another parameter?

Bruna

Looking all over again now, 0.2 is probably 1/5, which is in WEEKS – meaning 20% of the exposed leave the compartment weekly. But the entire model is in years.. so I don’t know why she put sigma = 0.2 there! if the model is in years, it should be 52/5?

Bruna

NEVERMIND HAHAHA, it has to be in weeks (=0.2), because this is just for the observation of the data! the model is in years indeed, but the original reports were per week, so we will ask the model to let us visualize the data in weeks even though we are modelling it yearly. Assuming sigma weekly is just for the observation of data, so it matches the Weekly Reports of the disease.

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