Gce Model Questions Vol1 2017 Biology Question 11

In a closed community of 10 000 people, an infectious disease spreads as follows: each infected individual makes on average 12 potentially infectious contacts per day, and the probability of transmission per contact is 0.02 for symptomatic cases. Thirty percent of infected individuals are asymptomatic and transmit at half the rate of symptomatic individuals; their infectious period lasts 7 days, whereas symptomatic individuals are infectious for 5 days. Calculate the basic reproduction number \(R_0\) for the disease and then determine the minimum proportion of the population that must be immunised with a perfectly effective vaccine to prevent an outbreak. Give your answer as a whole‑number percentage.