you must understand that as far as we know most people that have died from the virus already had weakened immune systems to some degree, or they already had pre-existing conditions.
Also environmental factors are 100% playing into this as well considering how stuffty the air quality is in major Chinese cities, and as well the fact that most of the deceased were elderly men that smoke, so it's not surprising they'd have poor immune systems. Their respiratory and cardiovascular functions are already forgeted to some degree.
Oh and after the outbreak China already notified the WHO which has since published sequenced RNA of the virus. As of currently iirc 26 genomes have been isolated.