Pope Francis is continuing to improve from a bout of double pneumonia, the Vatican said Thursday evening.

The 88-year-old pontiff had progressed from using a nasal tube for supplemental oxygen to alternating the tube with a mask that allowed for a more comfortable flow, according to a detailed update.

Doctors on Thursday still said Francis' "prognosis remains guarded," suggesting that they did not think he was out of danger.

Francis spent Thursday morning in respiratory therapy. Later, he prayed in the chapel of his private suite in Rome's Gemelli Hospital, where he also received the Eucharist. After that, the pope attended to Vatican work responsibilities.

Francis, the leader of the Catholic Church, was admitted to Gemelli Hospital on Feb. 14 with a case of bronchitis that soon worsened to double pneumonia. This hospital stay is his longest during his time as pope. He is prone to lung infections, having had part of a lung removed when he was a young man.

It is not yet clear how his illness will affect his participation in the Lenten season, which begins on March 5 on Ash Wednesday and leads up to Holy Week and then Easter, on which according to Christian tradition Jesus was resurrected in Jerusalem.

Some of the faithful who have journeyed to Rome to see the Vatican and possibly the pope have altered their plans and are now saying prayers for Francis outside Gemelli Hospital for his full recovery.

Lili Iparea Fernandez, from La Cruz, Mexico, traveled to Rome with other pilgrims from Mexico, hoping to participate in Francis' general audience this week. When that was canceled, she decided to pray for him outside the hospital instead.

"We firmly believe that the pope will recover because he is a very strong man," she said Thursday. "So I invite everyone to believe firmly, with certainty, with confidence, with hope that the pope is going to be well."

The pope's illness has prompted Catholics to gather in Vatican City, his native Argentina and other areas of the world to hold prayer vigils.

Francis has been pope since 2013 when his predecessor, Pope Benedict XVI, resigned.

Some information for this report came from The Associated Press, Agence France-Presse and Reuters.