# Polio Eradication Progress (1980-2020)

## Overview

This interactive globe visualization demonstrates one of the greatest public health achievements in human history: the near-eradication of polio through the Global Polio Eradication Initiative (GPEI). The visualization shows vaccination coverage progression across 70+ countries over 40 years.

## Visualization Features

### Interactive Timeline
- **Year Scrubber**: Slide through 1980-2020 to see vaccination coverage evolution
- **Play/Pause Controls**: Automatic animation showing decade-by-decade progress
- **Historical Milestones**: Key events displayed for each significant year

### Visual Encoding

**Color Scheme (Vaccination Coverage)**:
- Deep Red (#f44336): 0-19% coverage - Critical risk areas
- Orange (#ff9800): 20-39% coverage - Low coverage regions
- Yellow (#ffeb3b): 40-59% coverage - Moderate progress
- Light Green (#8bc34a): 60-79% coverage - Good progress
- Green (#4caf50): 80-100% coverage - Optimal protection
- Dark Green (#1b5e20): Certified polio-free countries

**Special Markers**:
- Green border (2px): Countries certified polio-free by their region's certification year
- Red border (3px) + Red fill: Endemic countries (Afghanistan & Pakistan in 2020)

### Interactive Features
- **Click any country**: View detailed vaccination statistics
  - Current year coverage
  - 1980 baseline coverage
  - 2020 final coverage
  - Total improvement percentage
  - Certification year (if applicable)
  - Endemic status (if applicable)
- **Globe rotation**: Automatic slow rotation (pauses on user interaction)
- **Real-time statistics**: Global coverage, certified countries, endemic count, cases prevented

## Data Sources

### Primary Data
- **WHO/UNICEF Estimates**: Coverage of third dose of diphtheria-tetanus-pertussis vaccine containing polio (DTP3) used as proxy for Pol3
- **GPEI Records**: Global Polio Eradication Initiative historical data
- **WHO Regional Certifications**: Official polio-free certification dates by region

### Coverage Methodology
Data represents the percentage of 1-year-old children who received three doses of polio vaccine (Pol3) for each year from 1980-2020. Coverage estimates are based on:
- Administrative data from national immunization programs
- WHO/UNICEF joint reporting forms
- Coverage surveys and demographic health surveys

### Regional Certification Dates
- **Americas**: 1994 (Last case: Peru, 1991)
- **Western Pacific**: 2000 (Including China, Australia, Pacific islands)
- **Europe**: 2002 (51 countries certified)
- **Southeast Asia**: 2014 (Including India - major milestone)
- **Africa**: 2020 (Wild poliovirus eradicated from continent)

### Endemic Countries (2020)
Only 2 countries remain with wild poliovirus transmission:
1. **Afghanistan**: 84% coverage in 2020, ongoing security challenges
2. **Pakistan**: 90% coverage in 2020, significant progress but transmission continues

## Key Historical Milestones

### 1980 - Pre-GPEI Era
- Global coverage: ~22% (estimated)
- ~400,000 polio cases annually worldwide
- Polio endemic in 125+ countries

### 1988 - GPEI Launch
- World Health Assembly resolution to eradicate polio
- Only 22% global immunization coverage
- Target: Eradication by year 2000

### 1991 - Americas Progress
- Last wild poliovirus case in Peru
- Western Hemisphere on path to eradication

### 1994 - First Regional Certification
- Americas certified polio-free by PAHO
- Demonstrated eradication was achievable

### 2000 - Western Pacific Certified
- China and Western Pacific region certified
- Massive achievement given population size

### 2002 - Europe Certified
- 51 European countries certified polio-free
- Further reduced endemic countries

### 2012 - India's Breakthrough
- India achieves 3 years without polio case
- Previously considered most challenging country

### 2014 - Southeast Asia Certified
- India's inclusion marks turning point
- Only 3 endemic countries remain (Afghanistan, Pakistan, Nigeria)

### 2020 - Africa Certified
- Wild poliovirus eradicated from African continent
- Nigeria (last African endemic country) certified
- Only Afghanistan and Pakistan remain endemic

## Impact Statistics (2020)

### Cases Prevented
- **20+ million** paralytic polio cases prevented since 1988
- **99.9%** reduction in global polio cases
- From 400,000 annual cases (1980s) to ~140 cases (2020)

### Vaccination Achievement
- **90%** global coverage in 2020 (up from 22% in 1988)
- **2.5 billion** children vaccinated through campaigns
- **184** out of 186 countries now polio-free

### Economic Impact
- $27 billion in treatment costs avoided
- $40-50 billion total economic benefits
- Prevented lifetime of disability for millions

## Technical Implementation

### Technologies
- **Mapbox GL JS v3.0.1**: Globe projection with atmosphere effects
- **GeoJSON**: Country polygon data with temporal vaccination properties
- **Vanilla JavaScript**: ES6 modules for clean architecture

### Mapbox Features Used
1. **Globe Projection**: 3D representation with atmospheric effects
2. **Dynamic Styling**: Choropleth with expression-based coloring
3. **Data-Driven Borders**: Variable width/color based on certification status
4. **Popups**: Interactive country details on click
5. **Fog Effects**: Space atmosphere for visual appeal

### Data Structure
Each country feature contains:
```javascript
{
  name: "Country Name",
  coverage_1980: 22,   // Baseline
  coverage_1985: 35,   // +5 years
  coverage_1990: 48,   // +10 years
  coverage_1995: 61,   // +15 years
  coverage_2000: 74,   // +20 years
  coverage_2005: 82,   // +25 years
  coverage_2010: 88,   // +30 years
  coverage_2015: 92,   // +35 years
  coverage_2020: 95,   // +40 years (final)
  polio_free_year: 2000,  // Certification year or null
  endemic: false          // true only for Afghanistan & Pakistan
}
```

## Educational Value

### What This Visualization Teaches

1. **Power of Vaccination**: Shows dramatic improvement from 22% to 90% global coverage
2. **Regional Approach**: Different regions certified at different times based on progress
3. **Persistence Required**: 32+ years from GPEI launch to near-eradication
4. **Final Mile Challenge**: Last 2 endemic countries show difficulty of reaching 100%
5. **Inequality Patterns**: Developed nations achieved high coverage faster than developing regions
6. **Success Story**: One of the most successful public health campaigns in history

### Notable Patterns

- **Americas led the way**: First region certified (1994), showing leadership
- **Western Pacific achievement**: Despite population size, certified by 2000
- **India's transformation**: From "impossible" to certified in 2014
- **Africa's triumph**: Overcame infrastructure challenges to certify in 2020
- **Final barriers**: Security, conflict, and access issues in Afghanistan/Pakistan

## Future Outlook

### Path to Eradication
- Focus on Afghanistan and Pakistan
- Improved security and access in conflict zones
- Continued high coverage in certified countries
- Surveillance for vaccine-derived poliovirus

### What Success Means
- Would be only the second disease eradicated (after smallpox)
- Annual savings of $1.5 billion in vaccination costs
- Blueprint for other disease eradication efforts

## Development

### Local Setup
1. Replace Mapbox token in `src/index.js`
2. Open `index.html` in web browser
3. No build process required - vanilla JavaScript

### Data Updates
To update data, modify `src/data/data.js`:
- Add new countries to features array
- Update coverage values for different years
- Adjust certification years as regions achieve polio-free status

## Credits

**Data Sources**:
- World Health Organization (WHO)
- UNICEF
- Global Polio Eradication Initiative (GPEI)
- CDC Global Immunization Division

**Visualization**: Mapbox Globe iteration 10
**Purpose**: Educational demonstration of vaccine impact and public health success
**Theme**: Vaccine-Disease Correlation Analysis - Polio Eradication

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*This visualization is part of a series exploring the relationship between vaccination campaigns and disease eradication efforts worldwide.*
