Comment by dtech

It's incredibly strong evidence that it's a required but not sufficient condition. I've seen professionals have serious suspicions that the single EBV-negative MS case from the study [1] OP mentioned was a false negative, but apparently it's not easy to confirm.

A single EBV-negative MS case. While there were 955 MS cases that developed in the 0.5M that were EBV-negative at the start of military service. You'd expect there to be about 50. That's pretty compelling evidence.

[1] https://www.usmedicine.com/clinical-topics/multiple-sclerosi...