Outbreak Basics (Chapter 1)
If R₀ = 1, what will happen to the outbreak?
The outbreak will neither grow nor decline. It will stay steady (each case replaces itself with one new case).
The Effective Reproduction Number (Rₜ) is the average number of secondary infections from one case in a fully susceptible population.
The Basic Reproduction Number (R₀) represents the average number of secondary infections that occur at time t, taking into account immunity and interventions.
True or False?
False
In the simple geometric progression model with R₀ = 3, how many new cases occur on Day 5 starting from one initial infection?
243 cases
According to the “Baby-Step Recipe” for building models, what is the first thing you must clearly state before adding compartments?
Answer: The outbreak question (e.g., early growth, peak timing, hospital load, intervention impact).
What is the typical “signature shape” of an epidemic curve when plotted over time?
Bell shaped curve with an Initial rise, a Peak, and Decline (to near zero)
In density-dependent transmission, what is the formula for the number of new infections per day in the SIR model?
β × S × I.
Policymakers often ask at the start of an outbreak: “Will the health system be overwhelmed if no action is taken?” Which key outbreak quantity does this question relate to?
Answer: The peak value of the epidemic (maximum daily cases)
Which type of transmission: density-dependent or frequency-dependent, is more appropriate for human respiratory infections like influenza, and why?
Answer: Frequency-dependent, because humans have a fixed number of daily contacts, so risk depends on the proportion of contacts that are infected, not total population size.
List four key epidemiological quantities in an epidemic curve and define anyone of your choice
Early growth rate (a proxy for R₀)
Peak (time and value of maximum incidence)
Final size (area under the curve ≈ total infections)
Capacity thresholds (e.g., hospital or ICU capacity lines)
Question: The basic SIR model can be extended in different ways. Compare SEIR and SIVR models:
What additional compartment is added in each case? (175 points)
What does that compartment represent/mean? (175 points)
Give one class of diseases for which each model would be appropriate. (150 points)
SEIR model: Adds an Exposed (E) compartment.
Represents individuals who are infected but not yet infectious (latent/incubation period).
Appropriate for diseases with a significant incubation period, such as measles, COVID-19, Chickenpox, Tuberculosis, HIV, Ebola virus disease, Hepatitis B and C, Rabies
SIVR model: Adds a Vaccinated (V) compartment.
Represents individuals who are immune due to vaccination rather than infection.
Appropriate for vaccine-preventable diseases, such as influenza, polio, Measles, Mumps, Rubella (MMR), Pertussis (Whooping cough), Hepatitis B, Tetanus, Diphtheria, and Pertussis, HPV (Human Papillomavirus), COVID-19, Smallpox, Cholera