The Vatican on Sunday released the first image of Pope Francis in hospital since he began treatment for double pneumonia, in which the 88-year-old pontiff appears to be breathing unaided.

The pope was admitted to Rome’s Gemelli hospital on February 14 with a severe respiratory infection that has required evolving treatment. He has not been seen in public since.

Francis is pictured from behind in the image as he is seated in a chapel at the hospital. The side of his face is visible and his right hand rests on his lap. He appears to be breathing on his own in the photo, after receiving oxygen throughout his treatment in hospital.

The Vatican said the pope had celebrated Mass with other priests in the chapel on Sunday.

The Vatican said in its latest medical update on the pope’s condition, issued on Saturday, that Francis was gradually improving and was reducing his use of mechanical ventilation at night to help with breathing.

The pope has been described as being in a stable or improving condition for nearly two weeks, but the Vatican has not yet given a timeframe for his discharge from hospital, saying his recovery is going slowly.

Francis is prone to lung infections because he had pleurisy as a young adult and had part of one lung removed.

The pope has been undergoing respiratory physiotherapy in hospital to help with his breathing and physical therapy to help with his mobility. He has used a wheelchair in recent years due to knee and back pain.

Francis, elected pope in 2013, celebrated his 12th anniversary from hospital on Thursday.

Doctors not involved in the pope’s care have said he is likely to face a long, fraught road to recovery, given his age and other medical conditions.

On Saturday, the Vatican announced that Francis had approved a new three-year process to consider reforms for the global Catholic Church, in a sign that he intends to continue on as pope, despite his health difficulties.