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