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.

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.

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

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.

Around the world, community, family and faith help physicians and medical advocates stay strong in the face of long hours and a relentless disease.

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