There are no 100 percent certainties in life, there is always a possibility that your cats could get out and be exposed to something. I've heard of EMT's coming in and out when someone is ill or injured accidentaly letting one out, or someone entering your house could have stopped to pet a kitty which was infected with one of the ailments that vaccines protect against. I wouldn't risk it with mine, but as one of your cats has had a reaction I would shop around and talk to different vets until I found one I was confident would take that reaction into consideration before vaccinating, and would take the utmost precautions to prevent a repetition. Having seen cats die one after the other of FLV, I would never care to see another one contract it, it isn't pretty, and isn't neccisary.
Jennie, Gary & our kids:
cat colony: Hunter S Tomcat, Archie and Mehitable, Witch, and Calamity Jane, Cuddlebug, Havana, Ghost, Spitfire Liz, Little Bit, Jesse, Moe, Cali, Stardust, Anastasia & Christy, Sally and the 5 boys
dog pack Heinz and Heidi
rip Tiger, Rabbit, Two Stars, Angel,Elaine, Mungo Jerry, Tex and Ijimus. I'll meet y'all at the bridge.