Lecture Notes on R Nought (R₀)

Definition of R Nought

• Pronunciation: Nought (N-O-U-G-H-T) is pronounced as "not."
• Meaning: Represents the number of new cases generated by an existing case, on average.
  • Formula: R₀ = Number of New Cases / Number of Existing Cases
  • Infectious Period: Varies by infection (days, weeks, years, decades).
  • Susceptible Population: Refers to non-vaccinated individuals or those who haven't encountered the infection before.

Examples of R Nought

• Infection A:
  • Initial cases: 4
  • New cases: 2
  • R₀ = 0.5
  • Outcome: Infection starts to die out.
• Infection B:
  • Initial cases: 4
  • New cases: 4
  • R₀ = 1
  • Outcome: Infection remains stable.
• Infection C:
  • Initial cases: 4
  • New cases: 8
  • R₀ = 2
  • Outcome: Infection spreads.
• Infection D:
  • Initial cases: 4
  • New cases: 72
  • R₀ = 18
  • Outcome: Infection spreads rapidly (similar to measles).

Implications of R Nought Values

• R₀ < 1: Infection will eventually die out.
• R₀ = 1: Infection remains stable over time.
• R₀ > 1: Infection will spread; the higher the value, the faster it spreads.

Examples of Specific Diseases

• Ebola: R₀ ≈ 2
• Measles: R₀ is significantly higher, making it more contagious than Ebola.

Interventions to Reduce Spread

• Block Transmission:
  • Isolate sick patients.
  • Use protective clothing for healthcare workers.
• Vaccination:
  • Example: MMR vaccine for measles.
  • Vaccines reduce susceptibility and prevent the spread of infections.

Conclusion

• R₀ is a critical measure in understanding the spread of infectious diseases.
• Preventative measures like isolation and vaccination can significantly reduce the spread of highly contagious diseases.