Pope Francis has shown a "further, slight improvement" in his medical condition, the Vatican said on Wednesday, in a sign of progress as the 88-year-old pontiff battles double pneumonia. The pope is spending his 13th night at Rome's Gemelli hospital,

The combination of health issues has kept the Pope from performing his public duties, including weekly prayers on Sundays, but his doctors have recently said he is alert, joking, and continuing to work, as well as reading messages from well-wishers around the world.

Concerns over Pope Francis' health have mounted in recent years as have questions about his succession. Here's what we know.