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EVEN MORE WORDS OF THE WEEK


WORDS OF THE WEEK – From standard epidemiology textbooks and from comments by Drs. Fauci and Birx, we have the several new terms. Many of the terms involve “constants,” which in every model and are always approximated at the on set.  Even the constant of gravity. All the so-called models you hear about involve these constants, and that is why early models are often inaccurate.

  • SIR model- Susceptible (those who can get it)-Infected (those who got it) -Removed (those who recovered). The SIR model is an equation that links these quantities. Important is there are constants of proportion for each disease most difficult to determine and usually approximated early in the epidemic (as we have sadly seen with COVID).
  • Epidemics - are commonly associated with acute, highly-transmissible directly transmitted pathogens that either kills its host or induce strong protective immunity.
  • Reproductive number R_0, average number of those newly infected from someone already infected
  • Effective reproductive number R_E; R_E = R_0 x fraction of susceptible. When R_E < 1, the epidemic is self-limited, i.e. fades away.
  • Latent period - Time from being infected to becoming infectious, i.e. the period from when you get it until you can transmit it.
  • Infectious period
    • Example: Influenza – latent period is one day with infectious period one-two days. Is quick to self-limit.
    • Example: Tuberculosis – latent period measured in decades with possible infectious period forever. Very slow to spread and become self-limiting (currently 8 million new cases per year).
  • Endemic - when transmission and demographic turnover rates are about the same. This means the disease persists,   e.g. tuberculosis, malaria, chicken pox, typhus, cholera, yellow fever.
  • Contagious vs Infectious. Contagious means the disease is spread through touch or through the air. Infectious means a disease that can spread from one person to another.
  • Variolation - process of inoculating a susceptible person with material taken from a vesicle of a person who has smallpox; first attempt at anything nearing a vaccination.
  • Vaccine - a substance put into the body, usually by injection, in order to provide protection against a disease. Smallpox is the first and only human pathogen to be eradicated through vaccination.


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