Epidemics

Question 1

factors determine severity: (4)

Answer 1

no. of infected people
severity of disease
vulnerability of certain groups
ease of which spread can = controlled/prevented

Question 2

Outbreaks
- ______ occurs in more numbers than usual
- _____ in community/area
- days to years-long

Answer 2

disease
contained

Question 3

What is an epidemic? (2)

Answer 3

• when infectious disease = rapidly spreads to many people
• affects larger area than outbreak

eg. Ebola + Zika Virus

Question 4

What is a pandemic? (3)

Answer 4

• geographical/global outbreak
• affects more people
• more deaths than epidemics
  eg. Spanish flu/Smallpox/HIV + AIDS/COVID-19

Question 5

What are the types of epidemic models? (6)

Answer 5

basic model - simple contagious epidemics
SIR model
SEIR model
Vital dynamics
SIRD model
SIRS model

Question 6

What is the SIR model? (4)

Answer 6

compartmental model - SIR

total population = N
susceptible people (large) = S
infected people (originally small) = I
recovered people (immune) = R

Question 7

What are the assumptions about the SIR model? (3)

Answer 7

• no births/deaths
  time = small enough
  fixed population size
• mild disease
  everyone recovers
  no deaths cause by disease
• complete immunity
  ≠ reinfection

Question 8

What is the LRD for the SIR model?

Answer 8

Question 9

N for SIR model =

Answer 9

Question 10

What is the function of the SIR model? (2)

Answer 10

• absolute quantities = ease of understanding
• normalising = adds abstraction

Question 11

beta =
gamma =

Answer 11

β
γ

Question 12

S =

Answer 12

∫ (- infection rate) dt

Question 13

I =

Answer 13

∫ (infection rate - recovery rate) dt

Question 14

R =

Answer 14

∫ (recovery rate) dt

Question 15

Infection rate =

Answer 15

Question 16

How does Beta affect the infection rate? (4)

Answer 16

= rate @ which S + I = come into contact
= probability of infection transfer - P(S converting to I)
= product of S and I
= depends on disease + population’s characteristics

Question 17

How does I/N affect the infection rate?

Answer 17

= proportion/rate of infected people
percentage of infected

Question 18

How does S affect the infection rate?

Answer 18

= no. of susceptible people

Question 19

Recovery rate

Answer 19

γ = rate of recovery
I = no. of infected people

Question 20

What are the important parameters of the SIR model? (2)

Answer 20

Ro
- basic reproduction number
- no. of infections 1 case generates (an average) over course of epidemic

Question 21

What is the formula for Ro?

Answer 21

Question 22

SIR model for I(0) =

Answer 22

Question 23

SIR model for
N = 1M
I(0) = 1
β = 0.2
γ = 0.1

Answer 23

Question 24

SIR model for
N = 1M
I(0) = 1
β = 0.16
γ = 0.1

Answer 24

Question 25

SIR model for β = 0.4 γ = 0.1

Answer 25

Question 26

What is the SEIR model? (5)

Answer 26

total population = N susceptible people (large) = S exposed people = E infected people (originally small) = I recovered people (immune) = R

Question 27

σ =

Answer 27

sigma - exposed to infected rate constant

Question 28

What is the LRD for the SEIR?

Answer 28

Question 29

SEIR model β = 0.4 γ = 0.1 σ = 0.2

Answer 29

Question 30

What does the model for vital dynamics include?

Answer 30

Vital dynamics: includes births + deaths

Question 31

What is the vital dynamics model?

Answer 31

total population = N susceptible people (large) = S infected people (originally small) = I recovered people (immune) = R β = beta γ = gamma μ = birth rate constant α = natural death rate constant

Question 32

What is the LRD for vital dynamics?

Answer 32

Question 33

Vital dynamics β = 0.4 γ= 0.1 μ= 0.004 α = 0.004

Answer 33

Question 34

What is the biggest difference for the SIRD model?

Answer 34

Not for mild diseases.

Question 35

What is the SIRD model?

Answer 35

total population = N susceptible people (large) = S infected people (originally small) = I recovered people (immune) = R deaths from disease = D β = beta γ = gamma μ = death rate constant

Question 36

What is the LRD for the SIRD model?

Answer 36

Question 37

SIRD model β = 0.4 γ = 0.1 μ = 0.004

Answer 37

Question 38

What is the biggest difference for the SIRS model?

Answer 38

NO complete immunity

Question 39

What is the SIRS model?

Answer 39

total population = N susceptible people (large) = S infected people (originally small) = I recovered people (immune) = R β = beta γ = gamma ζ = loss of immunity rate constant

Question 40

What is the LRD for the SIRS model?

Answer 40

Question 41

SIRS model β = 0.8 γ = 0.3 ζ = 0.004

Answer 41