Articles often state that certain SAR-COV-2 strains are more transmissible, e.g:
Most studies indicate Delta is 50-60% more transmissible than the Alpha variant
I believe that these studies are all based in statistics of people infected — that higher transmissibility has something to do with changes in the virus attachment and entry into human cells — but without much further detail. Is it known which changes lead to a virus strain becoming more contagious, and whether one can predict that when certain molecular changes appear in a virus strain it will be more contagious, or is our knowledge based solely on observation? Is it known which molecular changes make certain SARS‑CoV‑2 strains more contagious?