Year 9 Science · Unit 1 · Lesson 17
Challenge Worksheet
Learning Goals
What if…?
Scenario
Scientists at the Doherty Institute in Melbourne model a hypothetical new pathogen: "Pathogen X." It has an R₀ of 25, much higher than measles (R₀ ≈ 15) and far higher than COVID-19 (R₀ ≈ 3–5 for original strain). Pathogen X is a zoonotic spillover from bat populations in South-East Asia. Its most dangerous feature: infected individuals show no symptoms for 30 days, but they are highly infectious from day 5 onwards. By the time the first symptomatic cases are detected, a wave of invisible transmission has already occurred.
Box 1 Using R₀ = 25 and what you know about pandemic stages, predict how Pathogen X's trajectory would differ from COVID-19's in terms of: (i) how quickly it would progress from Stage 1 (emergence) to Stage 3 (amplification), and (ii) whether the "flatten the curve" strategy that worked for COVID-19 would be more or less effective. Justify your answer with specific reference to R₀ values and the 30-day silent incubation period.
Box 2 For COVID-19, contact tracing was effective in the early stages because symptomatic people could be isolated relatively quickly. Explain why a 30-day silent incubation period would make contact tracing dramatically less useful for Pathogen X. How would this change Australia's public health response strategy compared to its COVID-19 response?
Box 3 Pathogen X originated from bats through zoonotic spillover. Using your knowledge of how pandemics emerge and the role of international organisations like the WHO, propose three specific strategies that could be put in place nowbefore Pathogen X or anything like it actually appears, to detect and contain such a pathogen as early as possible. For each strategy, explain why the 30-day incubation and R₀=25 make it especially important.
1. The Black Death (1347–1351) and COVID-19 (2020) are both pandemics, but they differ enormously in how quickly they spread globally. Using specific evidence from this lesson about travel speed, transmission routes, and R₀, construct a detailed comparison of why the Black Death took years to spread across Europe while COVID-19 reached every continent in approximately 80 days. In your answer, define "pandemic" and explain whether both events meet the definition.
2. Ebola has a case fatality rate of approximately 50% and COVID-19 approximately 1–2%, yet COVID-19 became a global pandemic and Ebola did not. Using the relationship between lethality, transmissibility, incubation period, and R₀, explain scientifically why a very deadly disease does not automatically become a pandemic, and what combination of characteristics makes a pathogen most likely to cause one.
Wrap Up
In one sentence, what was the main idea of this lesson?