Yes there is an injection called Lufenuron. It last for 6 months of flea protection. It does not kill adult fleas, but rather controls fleas by interrupting their development by killing flea larva and eggs.
There is a newer kind of medication out called Capstar. This is an oral flea treatment that kills fleas in 30 minutes.
Let me know if you would like more information on flea treatments.
Sincerely, XXXXX
Expert in cat behavior and health
Expert in cat medical and behavior issues.