II. Definitions

  1. R0 (pronounced "R naught", or Basic Reproduction Number)
    1. R0 was derived by epidemiologist from its original use in organism reproduction (Basic Reproduction Number)
    2. R0 refers to the number of people that a single infected individual spreads to others
    3. R0 <1 suggests the infection will not spread broadly
    4. R0 >1 risks epidemic spread
  2. R (Effective Reproductive Number)
    1. R = R0 * X
    2. Where X is the percentage of the population that is susceptible to the infection
    3. Example: if 50% of the population is immune to the pathogen, X=0.5
    4. As with R0, when R <1, the infection will not continue to significantly spread
  3. Herd Immunity Threshold (HIT)
    1. Threshold over which a large percentage of the population's specific pathogen immunity protects the non-immune
    2. In general, approximately, HIT = 1-1/R0
    3. Example: If R0 = 5, HIT = 80%
  4. Serial Interval
    1. Time duration between symptom onset in a source patient (primary case) and symptom onset in a secondary case
  5. Incubation Period
    1. Duration between the time of infection (transmission) and the onset of disease symptoms

III. Precautions

  1. R0 is significantly modified by various environmental factors
    1. Immunization and Herd Immunity
      1. See Effective Reproductive Number (R) as above
    2. Crowding in large gatherings tends to increase R0 (depending on modes of transmission)
      1. Includes super spreading

IV. Interpretation: R0 and Herd Immunity Threshold (HIT) for Serious Infections

  1. Pandemic Influenza
    1. R0: 1.5-1.8
    2. HIT: 33 to 44%
    3. Serial Interval: 2-4 days
  2. Ebola
    1. R0: 1.5-2.5
    2. HIT: 33 to 60%
    3. Serial Interval: 10-16 days
  3. Covid19
    1. R0: 2-3
    2. HIT: 50-66%
    3. Serial Interval: 4-8 days
  4. SARS
    1. R0: 2-5
    2. HIT: 50-80%
    3. Serial Interval: 7-8 days
  5. Mumps
    1. R0: 4-7
    2. HIT: 75 to 86%
    3. Serial Interval: 18-20 days
  6. Smallpox
    1. R0: 5-7
    2. HIT: 80 to 85%
    3. Serial Interval: 18 days
  7. Polio
    1. R0: 5-7
    2. HIT: 80 to 86%
    3. Serial Interval: 2-45 days
  8. Rubella
    1. R0: 6-7
    2. HIT: 83 to 85%
    3. Serial Interval: 15-23 days
  9. Measles
    1. R0: 12-18
    2. HIT: 92 to 95%
    3. Serial Interval: 9-13 days

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Related Studies

Ontology: Incubation period (C1320226)

Concepts Finding (T033)
SnomedCT 406646006
English incubation period, incubation periods, Incubation period (observable entity), Incubation period
Spanish período de incubación (entidad observable), período de incubación