In conclusion, if adult FIV-infected cats that had been vaccinated previously are kept strictly indoors, the risk of being infected with other pathogens is likely lower than the possible harmful effect of vaccination. Ideally, antibody levels against FPV should be determined and FPV vaccination should only be considered in cats lacking protective antibodies. If antibody measurement is not possible, booster vaccinations in adult indoor-only cats, that have received previous vaccinations, are not recommended. If potential exposure to FPV, FHV, or FCV cannot be excluded, only core vaccines should be administered, preferably in an inactivated form.