i believe it is entirely possible that in times of poor health or when exposed to toxins or nutritional deficiencies, humans produce harmful dna/rna fragments (which we call viruses) we then shed these fragments from our mucosal surfaces (nose/mouth) and pass them to others where they are taken in and cause illness (and call this viral contagion) this model sits between the "no virus" theory and the standard virology model I began to formulate this thesis after reading about people "getting viruses while in space" after being quarantined and healthy prior to leaving earth. https://www.researchgate.net/profile/Joann-Silverstein/publication/300683635_Pathogenic_Viruses_in_Space_Indicators_and_Risks_in_Closed_Space_Environments/links/571fa5d308aed056fa235422/Pathogenic-Viruses-in-Space-Indicators-and-Risks-in-Closed-Space-Environments.pdf