Routes and dynamics of transmission: R0, incubation and infectious periods
Routes of transmission, R0 and the herd immunity threshold, incubation versus infectious periods, and how the timing of infectiousness against symptoms decides whether isolation, quarantine or vaccination controls an outbreak.
Tier 1Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Transmission depends on the route, how much organism a case sheds, how long they shed it, and how many susceptible people they meet.
- The basic reproduction number (R0) is the average number of secondary cases from one case in a fully susceptible population. The effective reproduction number (Re) accounts for immunity and control measures; an outbreak shrinks when Re is below 1.
- Herd immunity threshold = 1 − 1/R0. Measles (R0 12 to 18) needs about 92 to 94% immunity.
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Sources
- Australian Guidelines for the Prevention and Control of Infection in HealthcareAU/NZAustralian Commission on Safety and Quality in Health Care and NHMRC, 2019 edition, with subsequent dated updates; accessed November 2026
- CDNA Series of National Guidelines (SoNGs)AU/NZCommunicable Diseases Network Australia, Accessed November 2026
- Control of Communicable Diseases ManualAmerican Public Health Association, 21st edition, 2022
- Australian Immunisation Handbook: Measles; VaricellaAU/NZAustralian Technical Advisory Group on Immunisation (ATAGI), Digital edition, accessed November 2026
- Last updated
- 14 November 2026
What changed
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