Pope Francis, who is spending his sixth day in hospital for treatment of a respiratory infection, is alert and ate breakfast on Wednesday, the Vatican said in its latest update on the pontiff's fragile health.

"Let's all say a prayer for Pope Francis, who appears to have some serious health issues," said Vice President JD Vance on Tuesday.

Pope Francis has a “polymicrobial infection” of his respiratory tract that will require his hospital treatment to be changed, the Vatican said Monday, with tests indicating a “complex clinical picture” for one of the oldest popes in the church’s history.