A clinical vaccine candidate is able to replicate in host cells at low levels without causing disease symptoms. According to vaccine classification principles, which category does this candidate belong to and what is a likely clinical implication?

• A. Subunit peptide vaccine; because it replicates at low levels, it will generate long-lived cytotoxic T cell memory similar to live viruses
• B. Inactivated (killed) vaccine; typically requires no booster doses and induces robust mucosal IgA responses without safety concerns for immunocompromised hosts
• C. Live attenuated vaccine; tends to induce strong, broad immune responses including cellular immunity but may be contraindicated in severely immunocompromised individuals
• D. Replicating viral-vector vaccine that acts like an inactivated vaccine clinically and therefore needs no adjuvant or booster schedule in the general population

Answer: (C)