How effective is the vaccine now? When I was going through this, there was a significant percentage of non-effectiveness but that may have improved over the last several years. It was also around the time that vets were seeing a significant increase in vaccine-site sarcomas - that's why I stopped vaccinating mine, preferring one risk over another.

One thing I didn't think of in my previous response was the fact that the cat they are thinking of taking in has been a stray, which generally means he/she has had to develop a strong immune system to survive. That was another factor in my decision to allow my FeLV+ cat to share general space, the others had all been strays.