Should I vaccinate or neuter my cat during GS?

Vaccination or castration is not required during treatment. Healing the cat is paramount. There will be plenty of time after treatment to resolve the issue of castration. Personally, I am not a strong supporter of FVRCP vaccines (polyvalent vaccines) or the need to vaccinate cats against rabies (unless required by state or local legislation) or administering FeLV to cats that are at low risk for infection. If we treat a cat with FIP, it should be treated in accordance with standard professional care, locality (rabies) and your practice. In short, treat the cat like any other cat, but have it cured first.