I think the idea is not that there is a unique virus that is capable of causing symptoms in everyone exposed, but that there is a double- (or triple-) hit situation going on or that some other factor impacts the severity of illness as the result of infection. Perhaps PWME have genetic immune problems that make them less capable of handling the virus than most people, or that it takes multiple stressors at the same time or in close succession to make a PWME susceptible to a more serious infection from the virus. It's possible we are not able to clear the virus the way other people do.
There are known examples of pathogens affecting people very differently -- even people in close contact. Think about EBV and Burkitt's or Hodgkin's Lymphoma. Very few people get either of those diseases as a result of EBV infection, but some do as a result of genetic factors or combined infections. Another example is polio. Many people get it and clear it without consequence, but others have mild-severe consequences. IIRC, the factor is what tissues get infected. For example, my cousin is quadriplegic as the result of polio while her brothers who got ill at the same time have no known consequences from the infection.
While those cases are hit-and-run situations, it's not beyond the realm of possibility that any number of factors, immune dysfunction or location of infection for example, might make an infection enduring (or reactivating) in some people but not in others.
I completely understand this and agree with this as a possibility, but what @Hip and @unto have stated is something a quite different, that they are passing a virus that seems to affect a lot of people around them in a significant and long-term way.