The Program injection is the best thing ever - though I think a lot of vets cottoned onto the fact that it lasts & they lose sales on other anti flea tuff, so it can be hard to find a vet that does it now
it works by sterilising the fleas when they feed, so they don't breed & you never get an infestation again.
When it first came out I had both of my old cats done with it after a really bad infestation, so bad that DH turned into a big screaming girl as walking passed the cats favourite spot in the attic had his hairy legs COVERED in them
- it was awful they were everywhere & we didn't think anything was going to work bar DDTing the house - or moving out :(
had the jabs done, no other treatment needed & fleas all gone in 2 weeks & never came back - EVER
a few years later & my old cats have passed & we now have 2 rescue cats - we found it much harder to find a vet that did the jab & when we did, they told us it only lasted 6 months
our old cats lasted years - I thought perhaps the formula had been changed, but thought we'd wait & see if our current cats did get fleas before going back for the booster -
nearly 2 years later & they've not needed another jab, so it does look like it might be just sales pitch
I'd highly recommend it though :)