Epidemics, Globalization, and Culture

Vital Concepts and Terminology


Latency and Incubation

The latency period differs subtly but in an important way from the incubation period for some microbes. Both are indexed from the time of exposure.  

— The latency period refers to the time between exposure and infectiousness.

— The incubation period refers to the time between exposure and the first signs of disease.


This is most important in understanding of the most dangerous aspects of the recent HIV pandemic.

The latency period is quite short often only a few weeks from the time of infection. By contrast, the incubation period is quite long – often as long as several years.

HIV, greatly assisted by its long silent incubation period averaging eight to ten years, encircled the globe by using these networks before it was even recognized.


Immunity and Resistance


Immunity occurs within a single lifetime. It results from previous infection by the same disease, or one closely related. The immune system "remembers," and when exposed again, it rapidly extinguishes the invader.


This assumes that a person survived the first encounter with the disease. Vaccination is based on deliberately exposing people to mild or 'enfeebled' variants of a disease. This prepares the immune system for meeting the real-life, dangerous version.


Immunity may be full or partial. It may last a lifetime or just a few years. Immunity is not inherited and cannot be passed on to children. 


Smallpox vaccination, for example, confers immunity. But not lifelong immunity; it's good for 5-8 years. We all got vaccinated for smallpox, right? But that was a long time ago; the US stopped immunizing back in the 1970s. Your immunity is expired.



Resistance is genetic. A person is born with it― or not.  You get resistance from your ancestors.

SO: Immunity derives from your experience, resistance from your ancestors.


HERD Immunity

Group survival involves more than individual resistance or immunity.


Epidemiologists often use the term herd immunity to refer to two distinct protection mechanisms. Here the terms herd immunity and herd resistance are used.


Herd immunity occurs when an immune majority shields a minority of vulnerable individuals from contagion. 


Herd resistance is different and is the result of having a large population with plenty of genetic diversity. The population has many alternative versions of the genes that protect against infection. Some versions work better against one disease; other versions of the same genes work poorly against the first disease but act well against other infections. Different individuals carry different versions of these protective genes. Even if a totally new and highly virulent disease appears, a large, genetically diverse population will contain some individuals who are inherently resistant. 


Important point: the concept of "racial purity" constitutes a serious liability in the face of epidemic disease.