Inactivated vaccines differ from live vaccines because they:
Inactivated vaccines fundamentally differ from live attenuated vaccines because they cannot replicate within host tissues. Inactivation achieved by chemical agents formaldehyde crosslinking proteins, beta-propiolactone alkylating nucleic acids, heat denaturation destroying polymerase enzymes, while preserving epitopes for antibody recognition. Because genome destroyed, no progeny virions produced, infection cycle aborted, inability to cause disease even if host immunocompromised. Immunologically absence of cytosolic replication reduces engagement of RIG-I, MDA5 cytosolic sensors sensing replicating RNA, resulting in weaker type I interferon and CD8 T cell response primarily relying on exogenous antigen uptake presented via MHC II to CD4 helpers producing mainly humoral immunity. Duration shorter necessitating adjuvants like aluminum hydroxide forming depot, enhancing uptake by dendritic cells, activating NLRP3 inflammasome IL-1 beta release. Inactivated vaccines include IPV, HAV, influenza split, rabies. They exhibit increased safety, no shedding, no reversion, but require higher doses often multiple injections to achieve protective titers. Distinction impacts storage, contraindications and schedule design with more boosters required to maintain herd immunity threshold.
Ref: Baxter J Clin Virol 2007 Inactivated cannot replicate; Plotkin Inactivated vs Live difference; CDC.