When Benedict XVI became the first pope to resign in 600 years it sent shockwaves through the Catholic Church. Now, after spending two weeks in hospital battling pneumonia, the speculation in the Vatican is whether his successor Pope Francis might do the same.

Pope Francis has entered his fourth week in the hospital with double pneumonia. Francis has increasingly handed off his day-to-day duties to cardinals as questions swirl about the near- and long-term future of his papacy.

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

"The night was quiet, the pope was resting," the Holy See, the Vatican's press office, said in a brief statement on Sunday morning.

The Vatican said Pope Francis is showing "gradual, slight improvement." The 88-year-old has been in the hospital for 23 days, battling double pneumonia.