Judy Woodruff:

Last month, the U.S. Food and Drug Administration formally approved the first vaccine to prevent Ebola.

It comes at a crucial time. An outbreak in the Democratic Republic of Congo has infected more than 3,000 people since early last year. And yet the situation could be much worse.

What has prevented it from spiraling out of control is five years of remarkable scientific progress.

With the second of our series, again in partnership with the Global Health Reporting Center, here's special correspondent Monica Villamizar.