Basic reproduction number, herd immunity threshold, and outbreak transmission dynamics concepts for infectious disease epidemiology.
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- What does "R0" stand for in epidemiology?
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Basic reproduction number.- What does the basic reproduction number (R0) measure?
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The average number of secondary infections caused by one infected person in a fully susceptible population.- What is the effective reproduction number (Re or Rt)?
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The average number of secondary infections caused by one infected person in a population that is not fully susceptible.- If Re is greater than 1, what happens to an epidemic?
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It grows, case numbers increase.- If Re is less than 1, what happens to an epidemic?
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It declines, case numbers decrease.- If Re equals 1, what is the state of an epidemic?
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It is stable, case numbers stay roughly steady.- The herd immunity threshold formula is ____.
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1 - 1/R0- What is herd immunity?
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Indirect protection of susceptible individuals when enough of the population is immune to limit disease spread.- Name the three main factors that determine R0.
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Contact rate, probability of transmission per contact, and duration of infectiousness.- Approximately what is the R0 of measles?
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About 12 to 18.- Approximately what is the R0 of seasonal influenza?
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About 1 to 2.- Approximately what is the R0 of the original (ancestral) SARS-CoV-2 strain?
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About 2 to 3.- Approximately what is the R0 of smallpox?
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About 5 to 7.- A disease with a higher R0 generally requires what kind of herd immunity threshold?
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A higher herd immunity threshold.- Why can R0 not be measured directly?
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It must be estimated from data and models, since a fully susceptible population is rarely available to observe.
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