A December 2020 journal article I was using (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7751056/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7751056/) gave a

A December 2020 journal article I was using (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7751056/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7751056/) gave an r0 range of the original of 1.5-6.68 across various studies. https://pubmed.ncbi.nlm.nih.gov/34369565/ https://pubmed.ncbi.nlm.nih.gov/34369565/ puts Delta at about 5.08 and the origin strain at around 2.79. There is a lot of range in numbers I've seen, but the proportion is generally agreed to be about 2X for Delta to the origin strain. https://pubmed.ncbi.nlm.nih.gov/11742399 https://pubmed.ncbi.nlm.nih.gov/11742399 has smallpox between 3.5 to 6, so closer to Delta than the origin strain. I didn't look into these numbers to deeply as they seemed to be under active debate and my point was that smallpox is in the range of Delta, not the specific number.