The problem I'm having with the contagion theory is the explanation for transmission of some viruses takes a leap in logic giving "resonance" and unexplained universal phenomenon as the answer (The Contagion Myth - Thomas Cowan). "What really makes you ill" is a great read for the history and facts alone, I'm yet to get deep into the book and listening to "Virus Mania" on audible simulataneously. My current belief with germ/terrain theory is it's a combination that makes you susceptible to illness but i'm keeping an open mind. My family have a cold/flu at the moment and i've come down with a milder cold too so there's that...
there is not such a thing as virus. it is a boogeyman