Not long ago, the hospital in Tanzania where Dr. Namala Mkopi works was overwhelmed by sick children.
So many kids suffered from diseases like pneumonia and diarrhea, the hospital was often forced to assign two or more patients to a single bed.
Then, in 2012, Tanzania launched a nationwide campaign to vaccinate every child against pneumonia and rotavirus, two of the biggest threats to the country's kids.
Fast forward four years. When Dr. Mkopi flew to the US earlier this year, he says his hospital was empty as it has ever been.
Vaccines save lives. No one knows that better than Dr. Mkopi. Watch the video above to hear his story.