Pandemics Plagues and People

Exam 1

Latency Period

time interval from infection to

development of infectious (note: this definition differs

from that used for non-infectious diseases)

Infectious Period

time during which the host can infect another host

Incubation Period

Time between infection to development of symptoms

Symptomatic period

Period in which symptoms of the disease are present

Endemic

Habitual presence of a disease in a given geographic area

Epidemic

Occurrence of a group of illnesses of similar nature within a given community or region in excess of normal expectancy, and derived from a common or from a propagated source.

Pandemic

A worldwide epidemic

Herd Immunity

Resistance of a group of to an attack by a disease to which a large proportion of members of the group are immune.

What is R₀?

The average number of secondary cases caused by an infectious individual in a totally susceptible population. Indicates if a disease will spread or decline within a community/how fast/far transmission will occur. Higher R₀=bad

R₀ less than 1?

the disease will not spread and eventually die out

R₀=1?

the disease will remain stable in the community but will not cause an epidemic. One to one to one to one…..

R_{0 greater than 1?}

Disease will spread and may cause an epidemic. Example 1.5+1.5=3 people infected..etc

How does R_{0 relate to herd immunity}

•If R₀ is the mean number of secondary cases in a susceptible population, then

R is the mean number of secondary cases in a population where a proportion, p, are immune. Basically, •The higher R₀, the higher proportion of immune required for herd immunity

What are some things that decrease R0?

Screening, social distancing, tracking, handwashing, masking, quaratining, vaccination