1. It Hunts Us

In this introduction to life on the front lines, doctors in the U.S. and Asia battle the flu, and researchers race to develop a universal vaccine.

2. Pandemic Is Now

Vaccine debates rage while health-care workers inoculate against the Ebola virus in Congo and influenza in detainee camps at the U.S.-Mexico border.

3. Seek, Don't Hide

Worldwide, scientists test animals and their handlers for emerging viruses. In the U.S. and India, doctors work long hours caring for flu patients.

4. Hold On to Your Roots

Anti-vaccine debate escalates, and medical staff are attacked in Congo. Funding cuts hit hard in the U.S., but researchers in Guatemala make strides.

6. Don't Stop Now

Successes for some balance setbacks for others. Meanwhile, viral outbreaks continue to claim lives across the globe — and a larger pandemic looms.