1. Herd Immunity and Positive Externalities
by Jennifer Tontodonati and John Tibbetts
Slide 1: Diseases
Have you ever heard of these diseases?
Ebola
Measles
Mumps
Polio
Rubella

2. Slide 2: Data Collection
Red
Yellow
Green
Start
Round 1
Round 2
Round 3 – Start
Round 3 – End

3. Estimated R0 and HITs of well-known infectious diseases
Slide 3: Herd Immunity Threshold (HIT) Table
Estimated R0 and HITs of well-known infectious diseases
Disease
Transmission R0
HIT
Measles
Airborne
12-18
92-95%
Pertussis
Airborne droplet
12-17
92-94%
Diphtheria
Saliva
6-7
83-86%
Rubella
Smallpox
5-7
80-86%
Polio
Fecal-oral route
Mumps
4-7
75-86%
SARS
2-5
50-80%
Ebola
(Ebola virus epidemic - West Africa)
Bodily fluids
33-60%
Influenza
(Influenza pandemics)
33-44%
SOURCE:

4. Slide 4: Negative Externality Examples
Cigarette smoking creates passive smoking for non-smokers.
A loud concert at a park creates noise at a nearby quiet neighborhood.

5. Slide 5: Positive Externality Examples
Property values for other houses in the neighborhood rise when a homeowner improves his or her house and sells it for more than it was previously worth.
Recreation space is created when a state builds a reservoir for flood control.
An industrial company provides first aid classes for employees to increase job safety. An employee is also equipped to save lives outside the factory.

6. Slide 6: Vocabulary
Externality: A cost and/or benefit that spills over to a third party not directly involved in the production or consumption of a good or service.
Herd immunity: The resistance to the spread of a contagious disease within a population that results if a sufficient high proportion of individuals are immune to the disease, especially through vaccination.
Negative externality: A cost that spills over to a third party not directly involved in the production or consumption of a good or service.
Positive externality: A benefit that spills over to a third party not directly involved in the production or consumption of a good or service.