I’m not sure what this means

N0037003 Baby receiving the oral polio vaccine, Ethiopia
But it doesn’t sound good:

(NEWSER) – For nearly his entire life, a 29-year-old man living in the United Kingdom has had the polio virus living in his gut—where the strain has mutated from the weakened form he received in a vaccine as an infant to a much more virulent strain, according to a study published in PLOS Pathogens. It’s a case that NPR sees as “a worrisome new development in the polio end-game.” Live Science and the Guardian report the man was given an oral form of the polio vaccine at 5, 7, and 12 months. Unlike the injectable version, the oral vaccine uses a live virus that’s typically excised from the child’s gut within two months. But the man had an immune disorder that killed his gut’s ability to kill the virus. And so it has lingered there, and in his stool: More than 100 samples taken over the past 20 years have returned significant levels of what had become a mutated virus.