The vaxx wore off. He got the second shot, it looks, about 6 months ago. Vaxxes for influenza generally work (to the degree that they work) for 6 - 8 months. I’d expect little differences for vaxxes for what are essentially cold viruses (although, I can tell you from personal experience, I never had to be hospitalized for 2 days for a cold).
“hospitalized for 25 days.” not “2 days.”