English Language · English

Read the passage snippet and answer the question: 'The ecological processes that determine disease outbreaks to reach pandemic proportions are the size and distribution of population and movements of the infected and vulnerable hosts and disease-carrying viruses. The fact that five of the major 20 pandemics have occurred within the past 20 years speaks for itself about the effects of population explosion, rapid urbanization and increased life expectancy.' According to the passage, which of the following factors plays no role in a disease becoming a pandemic?