Vaccination prevents serious infectious diseases that cause significant suffering in unprotected cats; maintaining appropriate vaccination schedules throughout a cat's life is fundamental to welfare.
Preventive vaccination represents one of the highest-return welfare investments available for companion cats. The diseases prevented by vaccination cause significant acute suffering: panleukopenia is often fatal; calicivirus and herpesvirus cause chronic recurrent disease that impairs quality of life for years. The welfare cost of vaccination — a brief injection discomfort — is trivially small relative to the welfare benefit of disease prevention. Annual vaccination assessment with a vet also provides the health check opportunity to detect early disease signs.