PEORIA — Though 14-year-old Will Flynn won’t be starting high school at Peoria Notre Dame this fall, on Friday afternoon he was doing something he wasn’t able to do for a long time — ride a bike.

And he didn’t even need to take his oxygen tank.

Will, who was diagnosed with cystic fibrosis as an infant, had a double lung transplant June 8 at St. Louis Children’s Hospital. He and his father have begun riding bikes in parks all over St. Louis, including Forest Park, which is a short walk from the Ronald McDonald apartment where they’ve been living since April 21.

“The area we’re in is a lot like our neighborhood back home near Bradley Park, but take Bradley Park and times it by about 40,” said Jim Flynn during a phone interview Friday morning. “This weekend they are having a tribute to the World’s Fair, and we plan on going to that.”

The pair are enjoying the fact that Will has been feeling a lot better in the last couple weeks. Though the lung transplant went well from the get-go, Will suffered severe nausea from the powerful antibiotics he was being given as a prophylactic measure after the transplant — his doctors were concerned the drug-resistant strain of non-tuberculosis mycobacteria, or NTM, which destroyed his already compromised lungs, might have spilled into his blood during the transplant, said his father.

“We knew those drugs were going to make him sick, but it gave him his best shot,” said Jim Flynn. When tests showed no signs of NTM after 60 days, doctors discontinued the antibiotics, and Will started feeling better almost immediately. Since then he’s been working hard to get his strength back.

Will has been in and out of the hospital since late 2016, when he was diagnosed with NTM. Over the next two years, his hospitalizations grew closer together and his care more intensive. After 18 months of treatment for NTM, his lung function had dropped from 77% to 24%, and he weighed only 72 pounds. He was no longer attending school, and his doctors began to talk about a lung transplant.

Cystic fibrosis is something Will’s father knows a lot about — the youngest two of his five children suffer from the disease.

“Each parent has to be a carrier, and then there is a 25% chance that your child will have the gene,” said Jim Flynn. “It didn’t happen with the first three pregnancies, but it did happen with the fourth and fifth.”

Will’s older sister, Anna, also has CF. She’s also battling NTM, though so far it has been responding to treatment. Jim Flynn, who is divorced from his children’s mother, is the custodial parent.

“I don’t wake up with the disease, but I wake up with it next to me,” he said. “I’m constantly trying to understand the hurdles my children have to go through every day.”

Jim Flynn has been in St. Louis with Will for the past 117 days. He hasn’t gone home once. He’s been able to do that because of his employer’s vacation donation program. Flynn works as a first line supervisor at the Clinton Power Station.

“People have donated days so that I could remain here, which is incredible,” he said. “Without that piece in play, this would be a lot harder. I hope someday to give back to all the people who have supported me.”

Jim Flynn has also had lots of support from his wife and their extended family. On the day of Will’s 15-hour transplant surgery, about 30 people were on hand as the nurse provided periodic updates. At one point she called and said Will’s lungs had been removed, and offered to bring them into the waiting area.

“For so long I had a vision of what cystic fibrosis looked like, but this provided a truer meaning,” said the father. “I got to hold in my hands the struggle of my son’s past life and understand just how great a person he had to be to survive with those lungs that were doing virtually nothing for him.”

Normal lungs are pink. Will’s were purple.

“The doctors said that they had seen worse, but Will’s case was definitely one of the worst,” he said.

Five days after surgery, Will and his father removed his nasal cannula for a minute to see if he could maintain a normal oxygen level without assistance. He could.

“He looked down at his chest and he looked up at me and said, ‘This is impossible,’” said Jim Flynn. “He’s never able to breathe like a normal person. Now he says he doesn’t know what it’s like to struggle to breathe.”

Today the little backpack, with its load of oxygen and nasal cannula snaking over Will’s shoulder, is gone. And while he will always have cystic fibrosis, which can cause problems in other parts of his body, Will’s new lungs will not be affected, said his father.

The pair are looking forward to coming home to Peoria early in September. Though Will won’t start high school this fall, he is looking forward to being there for the second trimester in November. Will said he’s hoping to do something this spring that he hasn’t been able to do in three or four years.

“I want to run track.”

Leslie Renken can be reached at 686-3250 or lrenken@pjstar.com. Follow her on Twitter.com/LeslieRenken, and subscribe to her on Facebook.com/leslie.renken.