Pope Francis is responding “positively” to medical treatment for pneumonia, according to the Vatican, a week after the 88-year-old pontiff was hospitalized in Rome.

Pope Francis is being treated in hospital for double pneumonia — but what is this condition, and why might the pope be particularly vulnerable to it?

Pope Francis’ condition poses no immediate threat to his life though he remains at risk after a week in the hospital for treatment of pneumonia, doctors said.