-Derek Hale about Sarah Māhealani
In order to be a Eclipse wolf, the poor victim has to be bitten on a Lunar Eclipse. This type of bite is generally fatal.
If a person survives past the venom searing through their bloodstream(which is extremely painful in itself) The full moon transformation may kill them. Those lucky enough to survive are generally stronger than most werewolves, but rarely attain Alpha status.
Alpha's tend to avoid creating such wolves because of the high fatality rate.