George, 69, contracted polio at age 13; to this day, he wears a leg brace to support muscles ravaged by the viral illness. Felde, 58, caught the disease as an 11-month-old infant and has lived with its aftereffects since.
"As a fellow survivor, I'd like the cardinal to know: 'You're an amazing example to us all. And please, please, take care of yourself,'" said Felde of Downers Grove, Ill.
Medical experts say it's advice worth heeding. As the last Americans struck by polio advance into their senior years, the disease's residual impact is exacerbating the effects of aging and later-life illness, such as George's cancer.
That can pose new challenges to individuals who, like George, have dealt with their disability by refusing to let it define their identity or limit their sense of possibility.
"Most of my patients with polio are real Type A high achievers," said Dr. Irwin Siegel of Rush University Medical Center in Chicago, who has treated polio survivors since the 1950s. "They resist anything that labels them as handicapped, and they don't want lifestyle changes like working less.
"If they start getting weaker - which most do with age - their response is usually to try harder, which can backfire and make the weakness even worse. You have to convince them to back off and get some rest."
Easing up may be hard for George, who is used to overcoming obstacles and pushing himself to the limit. The cardinal plans to return to a full public schedule Oct. 1 and to make a demanding trip to Rome about two weeks later.
George is an extraordinarily disciplined man who exercises daily to keep muscles in his legs and trunk in shape, according to Colleen Dolan, a spokeswoman for the Roman Catholic Archdiocese of Chicago.
Although he "does not speak about his polio ... he's never wanted that to be the focus of his life ... it's very much a part of who he is," Dolan said.
One of the most feared diseases of the 20th century, polio largely disappeared from the United States after the Salk vaccine became available in the mid-1950s.
There are about 1.6 million American polio survivors, including 640,000 who had a more severe, paralytic form of the infectious illness, according to Dr. Julie Silver, director of the International Rehabilitation Center for Polio at Spaulding Rehabilitation Hospital in Boston.
This subgroup experienced the greatest damage to nerves and muscles and is at greatest risk later in life from polio's aftereffects, including weakness, fatigue and chronic pain.
Those complications don't represent a recurrence of polio; instead, they are the result of long-lasting deficits the disease left behind. An illness such as cancer can compound polio-related weakness, especially for people who undergo potentially disabling treatments or need extensive bed rest that can contribute to muscle atrophy.
"A real risk for the cardinal was a significant decline in his functional status, due to the combined effect of the cancer and the earlier polio," said Dr. James Sliwa, a polio and cancer rehab specialist at the Rehabilitation Institute of Chicago.
The challenge for George, the doctor suggested, will be to balance the need for activity with the need to conserve energy and prevent muscle overuse.
Scientists are still exploring what causes the late effects of polio. In addition to the natural effects of aging, there are two main theories, said Dr. Eric Sorenson, section head of neuromuscular diseases at the Mayo Clinic. One is that overtaxed motor neurons - cells that transmit messages to muscles - wear out over time. The other is that a continuing inflammatory reaction may slowly worsen muscle damage.
When someone is young, the body has a remarkable way of compensating for polio-related neuron loss: Unaffected neurons start doing double-duty, sprouting new shoots that activate nearby muscles. But with age, motor neurons begin to wear out and die, reducing the body's ability to adapt. Overuse may contribute to the deterioration.
"If you've got a lot of neurons in reserve, like most people do, you probably won't notice much difference," Siegel said. "But if you've had polio, your bank account of neurons will be severely depleted."
Then there are ailments related to the strain of compensating for a disability. "Someone who has worn a brace most of their life may be more vulnerable to arthritis or more likely to fall," said Silver, whose mother, grandfather and uncle caught polio just after the end of World War II.
Arms that have helped a polio survivor rise from a sitting position over the years may weaken. Knees that have borne the stress of an uneven gait may begin to give out. Wear and tear on a hip may contribute to what many polio survivors describe as "deep, burning, aching" muscle and back pain, Silver said.
For some, these symptoms are sufficiently far-reaching to merit a diagnosis of "post-polio syndrome." More than 300,000 Americans may suffer from this condition, which typically surfaces 15 to 30 years after an initial episode of polio, Silver estimates. There are no proven treatments other than lifestyle modifications.
Other survivors, such as George, aren't diagnosed with the syndrome but have episodes of difficulty related to their long-ago disease.
Patricia Morris, 67, who was hospitalized with polio for seven months in 1943 at age 4, says re-encountering the illness later in life takes an emotional toll.
"You can't believe this is happening to you again - it can't be," said Morris of Rolling Meadows, Ill. "You fought so hard to get where you were and you feel you can't lose it, so you fight harder. And the more you fight, the worse it becomes."
With years of physical therapy, Morris was able to walk with crutches and a brace, marry, have two children and work in an office. Then, in the 1980s, her legs began to weaken and her shoulders began to ache nonstop. Today, she can stand only for 30 seconds and uses a scooter to get around.
"What's the point of feeling sorry for yourself?" Morris asked. "You put it behind you and you go on."
Morris has watched George from afar over the years, wondering and worrying about his stamina and his very busy schedule. Now, she said she'll be paying particular attention, as the cardinal steps back into his role with the public's attention newly focused on his health.
"All I can think is, everyone is going to see him and know what he's had to go through," Morris said. "And that's something special for people like me who know what it's like."
Judith Graham writes for the Chicago Tribune.