LA CROSSE, Wis. (CNS) -- Cardinal Raymond L. Burke said he is continuing steady progress in his recovery from COVID-19, but explained that it is slow going in a letter to supporters and friends.

In a letter dated Sept. 25, the 73-year-old cardinal thanked people "with all my heart, for your faithful and generous prayers for the recovery of my health."

Cardinal Burke wrote that he has continued to recover in a house near family members in Wisconsin since his release from the hospital Sept. 3. A native of Richland Center, Wisconsin, in the La Crosse Diocese, Cardinal Burke has not disclosed where he was hospitalized.

"The house is well adapted for the rehabilitation program which I am following," he wrote.

The cardinal explained that his priest secretary had arrived from Rome to assist with his rehabilitation.

"He is also helping me respond to correspondence and to deal with the many schedule changes necessitated by the time I was in the hospital and now by the several weeks I will need to recover as fully as possible," Cardinal Burke wrote.

"Although I am making steady progress, it is slow," the letter continued. "The doctors and therapists who direct the program of rehabilitation assure that it is necessarily so and that I am doing well."

He said he was "trying to grow in patience" as he regains "certain fundamental physical skills needed for my daily living, and overcoming a general fatigue and difficulty in breathing," which are typical reactions to those who are recovering from the airborne coronavirus that causes the illness.

Cardinal Burke added that he was unsure when he would be able to conduct normal activities.

In the letter, the cardinal also credited God for saving his life "for some work he wishes me to carry out."

"I am determined to use the present time of rehabilitation in the best manner possible, so I will be prepared to carry out his work," the letter said.

Cardinal Burke concluded the letter by asking for prayer for a full recover and said he also offered his "prayers and sufferings" for those who have been praying for him and for the world and the Catholic Church, "which are beset with so much confusion and error to the great and even mortal harm of many souls."

The cardinal has not made it public knowledge on whether he was vaccinated for the novel coronavirus, which causes COVID-19.

The Vatican had started offering all Vatican residents, retirees and employees the vaccine developed by Pfizer and BioNTech in mid-January 2021. The cardinal was eligible for the vaccine as a member of the College of Cardinals and a member of the Apostolic Signatura, which he led as prefect from 2008 until his resignation in 2014.

Cardinal Burke has expressed concerns about the COVID-19 vaccines, including that it is "never morally justified to develop a vaccine through the use of the cell lines of aborted fetuses. The thought of the introduction of such a vaccine into one's body is rightly abhorrent."

He also said the "vaccination itself cannot be imposed, in a totalitarian manner, on citizens."

In December, the Vatican Congregation for the Doctrine of the Faith, citing church teaching, said that when alternative vaccines are not available, it is morally acceptable to receive vaccines developed or tested using cell lines originating from aborted fetuses, in this case, including COVID-19 vaccines.

The Pfizer and Moderna vaccines did not use abortion-derived cell lines in developing or producing their vaccines, but they did in lab testing.

Cardinal Burke served as bishop of the Diocese of La Crosse from 1995 to 2004, as archbishop of St. Louis from 2004 to 2008, and as prefect of the Vatican Apostolic Signature from 2008 to 2014.

While the cardinal often resides in Italy, he travels extensively and was in the United States at the time of sharing the news about contracting the virus.