The flanker, who moves up from the Senior Academy into the Saints first team squad later this year, injured his shoulder in November. However he is now back in action and racking up the minutes.
As well as playing in the Wanderers' recent win at Newcastle Harrison has been dual registered with Cambridge, playing in all the Blood and Sands' matches over the past month.
"It's good to be getting a run-out after four-and-a-half months out," he says. "It was a really frustrating time for me. Before I injured my shoulder I'd been pushing for a bench spot for the first team and now I'm back at ground zero and having to build myself up.
"But everyone at Franklin's Gardens was really supportive and wanting me to get back fit and playing, and pushing on. They've helped in loads of ways.
"You have to be hungry for the game and to want your spot back. But you can be too anxious and when it's your first game back for a few months you're excited to be back and sometimes can over-work yourself and give yourself an injury."
Playing for Cambridge has been a steep learning experience for Harrison. The team has had a challenging campaign, to say the least, with a mid-season change in coaching staff and a battle against the drop from National League One.
"It's been hard, but it's also been good for me," the 20-year-old commented. "It's a physical league, and while Cambridge have had a rough season they've got new coaches, are building back, and it's a good place for me to start.
"It's been helpful to be playing with Darrell [Dyer] and Will [Hooley]. It means that I've always got someone to talk to if I need to, but saying that the whole Cambridge team is a decent bunch of lads. Everyone's been welcoming and they're easy to get along with."
One of those new coaches at Cambridge, former All Blacks flanker Craig Newby, is a familiar face to Harrison. Like Harrison, Newby attended Rotorua Boys School and his All Blacks shirt hangs proudly in the school's corridors, and the youngster says that it is another useful source for his rugby education.
"Back at school his name and photos were all over the shop, and to be honest I was a bit star-struck!" Harrison says. "He's a good coach and I can learn a lot from him, especially because he played in my position as a flanker. I've got a lot of respect for him, and learning from him is like learning from the likes of Phil Dowson and Tom Wood, but this time he's my coach."
Harrison is in line to play for Cambridge again this weekend, and after having returned to the black, green and gold for the trip to Newcastle he is also hoping to get some more time against Saracens as he continues to work his way back to full match fitness, adding: "It was especially good to play in Saints colours for the Wanderers in the win at Newcastle.
"There's no other club that I'd rather play for, whether it's the Saints or the Wanderers, and I'm looking forward to hopefully playing against Saracens a week on Monday."