Question

What is the relationship between the Reproductive Rate (R₀) and the proportion of susceptible individuals that become infected with a disease? Is there a value below which almost no one becomes infected?

Answer 1

1 Reproductive ratio R0

IT IS THE AVERAGE NUMBER OF SECONDARY CASES PRODUCED BY ONE INFECTED INDIVIDUAL INTRODUCED IN TO A POPULATION OF SUSCEPTIBLE INDIVIDUALS .HERE INFECTED ARE DISEASED AND SUSCEPTABLE ARE HEALTHY R0 USED IN DETERMINING IF AN EMERGING INFECTIOUS DISEASE SPREAD IN A POPULATION AND DETERMINING WHAT PORTION OF THE POPULATION SOULD BE IMMUNISED TO ERADICATE DISEASE

NOT ALL CONTACTS WILLBE SUSCEPTABLE IN A POPULATION MAY BE DUE TO VACCINATION OR PRIOR INFECTION THEN THIS AVERAGE NUMBER WILL BE LOWER THAN R0 THIS IS EFFECTIVE REPRODUCTION NUMBER OR RTHAT IS EFFECTIVE REPRODUCTION NUMBER IS THE AVERAGE NUMBER OF SECONDARY CASES PER INFECTIOUS CASE IN A POPULATION MADE UP OF BOTH SUSCEPTABLE AND NON SUSCEPTABLE HOST THIS CAN BE ESTIMATED BY THE PRODUCT OF BASIC REPRODUCTIVE NUMBER AND FRACTION OF HOST POPULATION SUSCEPTABLE

Re= R0X HERE R IS EFFECTIVE REPRODUCTION NUMBER

R0 IS REPRODUCTIVE RATIO

X IS FRACTION OF HOST POPULATION it can also written as Re=R0X(S/N) here S/N is the suseptable INDIVIDUALS

IF R0 IS 18 AND HALF OF POPULATION IMMUNISED THEN R=18X.5 =9

SINGLE CASE PRODUCE 9 NEW CASE

2 R0<1 CAUSE LESS THAN ONE NEW INFECTION