Pope Francis has the onset of double pneumonia, the Vatican said on Tuesday, complicating treatment for the 88-year pontiff and indicating a further deterioration in his fragile health.

Francis has been suffering from a respiratory infection for more than a week and was admitted to Rome's Gemelli Hospital on February 14.

The Vatican said in a statement that the pope had undergone a chest CAT scan on Tuesday afternoon which had revealed "the onset of bilateral pneumonia that requires further pharmacological therapy".

Bilateral pneumonia is a serious infection that can inflame and scar both lungs, and makes breathing more difficult.

"Laboratory tests, chest X-ray, and the clinical condition of the Holy Father continue to present a complex picture," the Vatican said.

It reiterated that the pope was suffering from a "polymicrobial infection", saying this required corticosteroid and antibiotic therapy, which was "making treatment more challenging".

"Nevertheless, Pope Francis remains in good spirits," the Vatican statement added.

The pope is especially prone to lung infections because as a young adult he developed pleurisy and had part of one lung removed.

A Vatican official, who declined to be named because of the sensitivity of the issue, said earlier in the day that the pontiff had not been put on a ventilator and was breathing on his own.

Ahead of the latest statement, the Vatican announced that all public engagements on the pope's calendar had been cancelled through Sunday.

The pope had been due to lead several events over the weekend for the 2025 Catholic Holy Year, which runs through to next January.

The Vatican said on Monday that doctors had changed the pope's drug therapy for the second time during his hospital stay to tackle a "complex clinical situation".

Doctors say a polymicrobial infection occurs when two or more micro-organisms are involved, and can be caused by bacteria, viruses, or fungi.

The Vatican has said Francis will stay in hospital for as long as necessary.

The pope has been plagued by ill health in recent years, including regular bouts of flu, sciatica nerve pain and an abdominal hernia that required surgery in 2023.

The Vatican statement on Tuesday said he was grateful for all the support he has received in recent days. "With a thankful heart, (he) asks for continued prayers on his behalf," it added.