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 marked the one-week point Friday in his hospital stay, getting up to eat breakfast as the 88-year-old pontiff continued fighting pneumonia and a complex respiratory infection, the Vatican said.