basic reproductive number

1. Basic reproductive number (Ro)

2. Outline
• Measures of transmissibility
• Definition: BRN
• BRN v/s SAR
• Effective reproductive number (Re)
• Re & the epidemic curve
• Re & herd immunity

3. Measures of transmissibility
• Attack rate
• Secondary attack rate (SAR)
• Basic reproductive number (Ro)
• Effective reproductive number (Re)

4. Basic reproductive number (R0):
• Number of absolute new cases which arise from a single case

6. Is there any difference between R0 and SAR?

7. Effective reproduction number (Re):
• Total number of new cases which arise from a single case with
adjustment for
Density
Immunity
Susceptible population

8. • Re = 1 (Endemic)
• Re > 1 (Epidemic)
• Re < 1 (disease can die out)

10. Re & herd immunity
•Herd immunity = 1 – (1 ÷ Re)

12. Summary
• The basic reproductive number is a core measure of disease
transmissibility
• It is a function of both disease and context
• The value of Ro determines if cases of a disease are rising, declining, or
fading

13. To explore more:
• https://www.washingtonpost.com/graphics/2020/world/corona-
simulator/
• Oxford textbook of global public health