Ah, I see. I'm guessing you meant to say that if viruses don't exist, how can smallpox exist, full stop. Your adding that it was caused by a virus got me to focus on the fact that you hadn't shown strong evidence of that assertion.
Anyway, I don't claim to know the specifics as to what causes smallpox, but I do believe that I know the general outline of its cause, as well as the cause of any other disease- toxicity, malnutrition and stress. Have you heard of Terrain Theory? It arose at around the same time as Louis Pasteur's Germ Theory. There are plenty of articles on it online, I personally like the following one:
Germ Theory Versus Terrain: The Wrong Side Won the Day | westonaprice.org
Quoting the relevant passage:
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Béchamp’s various discoveries led him to conclude that our bodies are, in effect, “miniecosystems.” When an individual’s internal ecosystem becomes weakened—whether due to poor nutrition, toxicity or other factors—it changes the function of the microbes that are naturally present in the body, producing disease.20 In other words, microorganisms only become pathogenic after environmental factors cause the host’s cellular “terrain” to deteriorate.15
As one example of the powerful influence of weakening forces on the host’s ecosystem, a mid-1980s study looked at French children who experienced complications of wild-type varicella (chickenpox).22 (Note: France has never implemented varicella vaccination.) Although three deaths resulted from what is ordinarily an extremely benign childhood illness, all three fatalities took place within a subset of nine children who had been taking steroid medications on a long-term basis. In comparison, ninety-four previously healthy children recovered from varicella without incident. The researchers concluded that the deaths occurred “as a function of the [weakened] terrain.”
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I'm pretty sure you don't think that people don't actually exist. If you'd like an hour and a half of doctors going over fine points as to what's missing in terms of evidence for viruses, I invite you to take a look at the hour and half video from Dr. Sam Bailey, her husband Dr. Mark Bailey and Dr. Tom Cowan here. And in case you're wondering, yes, I saw the whole thing myself:
Baileys & Cowan Respond to Kevin McKernan | drsambailey.com