PPH4813 ASSIGNMENT 2 2026
DUE 15 MAY 2026
1. Describe the following epidemiology terms in relation to Rubella
Rubella (German measles) is a vaccine-preventable disease that illustrates key
epidemiologic concepts (CDC, Lesson 1, pp. 1-2).
1.1 Herd immunity
Herd immunity is the indirect protection of a population when a high proportion of
individuals are immune to an infection, thereby reducing the likelihood of transmission
(Merrill, 2017, Chapter 3, p. 54). For rubella, the herd immunity threshold is estimated at
83–85% (CDC, Lesson 1, p. 55). This protects pregnant women and others who cannot
be vaccinated.
1.2 Outbreak
An outbreak is an epidemic limited to a localised increase in disease incidence (CDC,
Lesson 6, p. 3). A rubella outbreak would be a sudden increase in cases in a specific
school or community above expected levels.
1.3 Epidemic
An epidemic is the occurrence of more cases of disease than expected in a given area
or among a specific group over a particular time period (Merrill, 2017, Chapter 1, p. 5).
Widespread rubella in a region, such as the 1964-1965 U.S. epidemic, is an example.
, 1.4 Pandemic
A pandemic is an epidemic that spreads over several countries or continents (CDC,
Lesson 1, p. 72). Before vaccination, rubella periodically affected many countries
worldwide, approaching pandemic proportions.
1.5 Endemic
Endemic refers to the constant presence or usual prevalence of a disease in a
population (Merrill, 2017, Chapter 1, p. 5). Rubella was endemic in the United States
before vaccine licensure in 1969, with seasonal peaks every 6-9 years.
1.6 Sporadic
Sporadic describes a disease that occurs infrequently and irregularly (CDC, Lesson 1,
p. 72). With high vaccine coverage, rubella is now sporadic in many developed
countries.
1.7 Cluster
A cluster is an aggregation of cases grouped in place and time that is suspected to be
greater than expected, even when the expected number is unknown (CDC, Lesson 6, p.
3). Two or three rubella cases in the same neighbourhood within a week would
constitute a cluster.
1.8 Incidence
Incidence refers to the occurrence of new cases of disease in a population over a
specified period (Merrill, 2017, Chapter 4, p. 74). Rubella incidence in the U.S. fell by
>99% after vaccine introduction because of effective immunisation programmes.
DUE 15 MAY 2026
1. Describe the following epidemiology terms in relation to Rubella
Rubella (German measles) is a vaccine-preventable disease that illustrates key
epidemiologic concepts (CDC, Lesson 1, pp. 1-2).
1.1 Herd immunity
Herd immunity is the indirect protection of a population when a high proportion of
individuals are immune to an infection, thereby reducing the likelihood of transmission
(Merrill, 2017, Chapter 3, p. 54). For rubella, the herd immunity threshold is estimated at
83–85% (CDC, Lesson 1, p. 55). This protects pregnant women and others who cannot
be vaccinated.
1.2 Outbreak
An outbreak is an epidemic limited to a localised increase in disease incidence (CDC,
Lesson 6, p. 3). A rubella outbreak would be a sudden increase in cases in a specific
school or community above expected levels.
1.3 Epidemic
An epidemic is the occurrence of more cases of disease than expected in a given area
or among a specific group over a particular time period (Merrill, 2017, Chapter 1, p. 5).
Widespread rubella in a region, such as the 1964-1965 U.S. epidemic, is an example.
, 1.4 Pandemic
A pandemic is an epidemic that spreads over several countries or continents (CDC,
Lesson 1, p. 72). Before vaccination, rubella periodically affected many countries
worldwide, approaching pandemic proportions.
1.5 Endemic
Endemic refers to the constant presence or usual prevalence of a disease in a
population (Merrill, 2017, Chapter 1, p. 5). Rubella was endemic in the United States
before vaccine licensure in 1969, with seasonal peaks every 6-9 years.
1.6 Sporadic
Sporadic describes a disease that occurs infrequently and irregularly (CDC, Lesson 1,
p. 72). With high vaccine coverage, rubella is now sporadic in many developed
countries.
1.7 Cluster
A cluster is an aggregation of cases grouped in place and time that is suspected to be
greater than expected, even when the expected number is unknown (CDC, Lesson 6, p.
3). Two or three rubella cases in the same neighbourhood within a week would
constitute a cluster.
1.8 Incidence
Incidence refers to the occurrence of new cases of disease in a population over a
specified period (Merrill, 2017, Chapter 4, p. 74). Rubella incidence in the U.S. fell by
>99% after vaccine introduction because of effective immunisation programmes.
