Practice question

Live attenuated vaccines developed through classical virology approach reducing pathogenicity while retaining replicative capacity that mimics natural infection without causing severe disease. Attenuation strategies include serial passage in heterologous host cells like chick embryo fibroblasts, embryonated eggs, or at subphysiologic temperature 25 to 33 degrees cold adaptation accumulating adaptive mutations in polymerase genes L and P reducing transcription efficiency in human cells at 37 degrees, plus mutations in surface glycoprotein cleavage sites reducing fusogenicity and in interferon antagonism proteins NS1 and V impairing immune evasion. Resulting strain enters mucosal epithelia via natural route intranasal or oral, expresses entire antigen repertoire including conformational fusion protein prefusion state, matrix and nucleoprotein providing CD8 epitopes conserved across strains that are destroyed by formalin inactivation crosslinking fusion peptide, and replicates limitedly to titers 10^3 to 10^4 increasing antigen dose tenfold from inoculum. This mechanistic insight supports diagnostic and therapeutic applications while reinforcing core immunological and cell biology principles taught in advanced curricula.