Influenza (flu) as an example of a viral disease

Pathogenic Diseases – Disease and Geography (Cambridge AS & A Level)

Geographers examine where diseases occur, why patterns differ, and how societies respond. The following notes use **influenza (the flu)** as a model viral disease and are organised to map directly onto the eight key concepts required for Paper 4 – “Disease and Geography”.

Key Concepts Mapping

• Scale – influenza operates from local outbreaks (e.g., a university) to regional waves (Southeast Asia) and global pandemics (1918, 2009).
• Place – incidence varies with climate, urban form, and health‑system capacity.
• Change over time – seasonal peaks, historical pandemics, and the accelerating speed of spread due to modern transport.
• Cause‑and‑effect – temperature, humidity, population density, mobility and health‑system resources affect transmission probability and contact rates.
• Systems – interaction of virus, human behaviour, environment and health services determines outbreak outcomes.
• Environmental interactions – climate and built environment modify droplet/aerosol survival.
• Diversity, equality & inclusion – burden differs by age, income, gender and ethnicity.
• Challenges & opportunities – vaccine development, surveillance networks, and equitable access to interventions.

1. What Is Influenza?

• Acute respiratory infection caused by influenza viruses (types A, B and C).
• Highly contagious; severity varies with age, health status and location.
• Seasonal influenza occurs each year; pandemic influenza arises when a novel strain spreads globally.

2. Virus Overview (Brief Biomedical Context)

Only the features that influence geography are needed.

• Enveloped, negative‑sense RNA virus with 8 segmented genes (A & B). Segmentation enables reassortment → new strains.
• Key surface proteins:
  • Hemagglutinin (HA) – binds to respiratory cells; determines host specificity.
  • Neuraminidase (NA) – releases new virions; target of antivirals (e.g., oseltamivir).

3. Transmission Pathways

1. Droplet transmission – large particles, travel ≤ 1 m, require close contact.
2. Aerosol transmission – small particles, remain suspended for minutes, can travel several metres.
3. Fomite transmission – contaminated surfaces, indirect transfer via hands.

4. Basic Epidemiological Measures

• Incidence – new cases per 100 000 population in a given period.
• Prevalence – total active cases at a point in time.
• Case‑fatality rate (CFR) – deaths ÷ confirmed cases.
• Basic reproduction number (R₀):

  R₀ = β × c × D

  • β = transmission probability per contact (influenced by climate, strain).
  • c = average contacts per person per day (higher in dense urban areas, schools, mass gatherings).
  • D = infectious period (≈ 5‑7 days for seasonal flu).

  Typical values: seasonal flu R₀ ≈ 1.2‑1.8; pandemic strains > 2.5.

5. Geographical Distribution & Drivers of Spatial Variation

5.1 Global Patterns

• Temperate regions (high‑income) – distinct winter peaks (Dec–Feb in the North, Jun–Aug in the South).
• Tropical regions (low‑ and middle‑income) – less pronounced seasonality; peaks often align with rainy seasons or school terms.

5.2 Drivers of Spatial Variation (Why Patterns Vary)

5.3 Scale of Analysis

• Global – Pandemic spread via international air travel; WHO Global Influenza Surveillance and Response System (GISRS) monitors evolution.
• Regional – 2009 H1N1 moved across Southeast Asia within weeks, amplified by dense megacities and regional flight networks.
• Local – 2018 outbreak at a UK university (> 300 cases) where crowded lecture halls and low vaccination increased contacts.

5.4 Change Over Time – Historical Pandemics

Trend: Mortality rates have fallen thanks to better health care, but the speed of global spread has accelerated with modern transport.

6. Impacts of Influenza – Geographical Perspective

6.1 Health Impacts

• Acute symptoms: fever, cough, sore throat, myalgia.
• Complications: viral/bacterial pneumonia, exacerbation of chronic diseases, higher mortality in very young, elderly and immunocompromised.
• Spatial inequality – higher CFR in low‑income regions (often > 2 %) compared with high‑income regions (< 0.1 %).

6.2 Economic Impacts

• Direct costs: hospitalisation (average £3 500 per admission in the UK), antiviral drugs, annual vaccination programmes (≈ US$1 billion globally).
• Indirect costs: absenteeism (average 3‑5 working days per case), estimated GDP loss of 0.1‑0.3 % during severe seasonal peaks (e.g., 2017‑18 flu season in the EU).

6.3 Social Impacts

• School closures, cancellation of public events, and stigma towards infected individuals.
• Disruption of essential services (e.g., reduced staffing in hospitals, transport).

6.4 Environmental Impacts

• Increased use of disposable personal protective equipment (PPE) and cleaning chemicals.
• Potential rise in antimicrobial resistance due to widespread antiviral use.

6.5 Diversity, Equality & Inclusion

• Age – children and the elderly experience the highest attack rates and severe outcomes.
• Income – low‑ and middle‑income countries often have <10 % vaccination coverage versus > 50 % in high‑income nations.
• Gender & ethnicity – occupational exposure (e.g., health‑care workers, informal sector) can create gendered risk patterns; minority groups may face barriers to vaccination.

7. Control and Prevention – Evaluation of Strategies

1. Vaccination
   • Annual reformulated vaccine targeting predicted circulating strains.
   • Strengths: Reduces incidence by 40‑60 % in well‑covered populations; lowers hospitalisation and mortality.
   • Weaknesses: Strain mismatch can drop effectiveness (< 30 %); limited access in low‑income settings; requires annual logistics.
2. Antiviral drugs (e.g., oseltamivir)
   • Neuraminidase inhibitors shorten illness if started within 48 h.
   • Strengths: Useful for high‑risk patients and outbreak containment.
   • Weaknesses: Costly, risk of resistance, dependence on early diagnosis.
3. Non‑pharmaceutical Interventions (NPIs)
   • Hand hygiene, respiratory etiquette, face masks, physical distancing, ventilation, school closures.
   • Strengths: Immediate, low‑cost, effective where medical resources are scarce.
   • Weaknesses: Compliance varies; socio‑economic costs (lost education, reduced commerce).
4. Surveillance & Reporting
   • WHO GISRS, national sentinel sites, rapid viral sub‑typing.
   • Strengths: Early detection enables timely vaccine updates and targeted NPIs.
   • Weaknesses: Dependent on laboratory capacity; under‑reporting in resource‑poor regions.
5. Policy & International Coordination
   • Travel advisories, pandemic preparedness plans, stockpiling of antivirals, joint research initiatives.
   • Strengths: Reduces duplication, shares expertise, mobilises resources.
   • Weaknesses: Political disagreement, inequitable resource distribution, implementation gaps.

8. Case Studies for Comparative Analysis

8.1 1918 Spanish Flu (Global Scale)

• Rapid spread via WWI troop movements; three waves in 1918‑19.
• ≈ 50 million deaths; highest mortality in 20‑40 year olds.
• Limited public‑health response highlighted the need for global surveillance.

8.2 2009 H1N1 Pandemic (Regional & Global)

• Originated in North America; reached all continents within six months.
• Higher infection rates in children and young adults; overall CFR ≈ 0.02 %.
• Accelerated vaccine production (WHO‑prequalified) and coordinated mitigation guidelines.

8.3 2018 University Outbreak – Local Scale (UK)

• 300+ confirmed cases on a single campus.
• Drivers: crowded dormitories, shared study spaces, low vaccination uptake (≈ 30 %).
• Control: temporary class suspension, targeted vaccination clinic, intensified cleaning, and communication campaign.

9. Systems Diagram (Textual Description)

10. Summary Points (Key‑Concept Checklist)

• Scale: Local (campus), regional (Southeast Asia), global (pandemic).
• Place: Climate, density, mobility and health‑system capacity shape spatial patterns.
• Change over time: Seasonal peaks, historic pandemics, faster global spread with modern transport.
• Cause‑and‑effect: Low temperature & humidity ↑ β; high density & mobility ↑ c; strong health systems ↓ D and CFR.
• Systems: Virus ↔ human behaviour ↔ environment ↔ health services.
• Diversity & Equality: Burden higher in low‑income groups, the very young, the elderly, and certain occupational/ethnic groups.
• Evaluation: Vaccination most effective where coverage is high; NPIs essential where resources are limited; surveillance underpins all strategies but requires equitable investment.