Our area is having a major flea infestation and our cats are indoor/outdoor cats. We did apply a topical over 3 weeks ago on the cats, I vacuumed and sprayed every inch of my 2000 square foot home. But yesterday I noticed the cats were still bringing in fleas? And everywhere I read I need to vacuum constantly. Will the spray continue to be effective for up to 7 months if I'm constantly vacuuming?