I don't think that's the most important factor. Influenza, along with ebola and rabies, is small, while smallpox is big. http://www.lehigh.edu/~jas0/viralgeno

I don't think that's the most important factor. Influenza, along with ebola and rabies, is small, while smallpox is big. http://www.lehigh.edu/~jas0/viralgenomes.html http://www.lehigh.edu/~jas0/viralgenomes.html