ROME >> The Vatican on Sunday released the first photograph of Pope Francis in more than a month, showing the pontiff in a three-quarter view from behind wearing a purple stole typical of Lenten liturgical vestments and sitting in a wheelchair before the altar of his personal hospital chapel.

The Vatican said he was participating in the celebration of the Mass with other priests in the 10th-floor papal apartment in the Gemelli hospital. No one else is visible in the photo and it is the first mention the Vatican has made of the pope’s participation in celebrating Mass since his Feb. 14 hospitalization for a bout with chronic bronchitis that quickly turned into double pneumonia.

There was no obvious sign that he was receiving supplemental oxygen mentioned in medical bulletins.

Doctors this week said the pontiff was no longer in critical, life-threatening condition, but they have continued to emphasize that his condition remained complex due to his age, lack of mobility and the loss of part of a lung as a young man. In an audio recording released March 6, the pope spoke in a feeble and labored voice as he thanked the faithful in St. Peter’s Square for their prayers.

His condition has been gradually improving over the last week, leading the Vatican to suspend morning updates and to issue less frequent medical bulletins. An X-ray this week confirmed that the infection was clearing.

In the most recent bulletin on Saturday, doctors said they were working to reduce the pope’s reliance on a non-invasive ventilation mask at night, which will allow his lungs to work more. He was continuing to receive high-flow supplemental oxygen, delivered by a nasal tube, during the day — although no such apparatus was evident in the photograph.