Inactivated vaccines usually require:
Inactivated vaccines usually require multiple doses and periodic boosters to achieve and sustain protective immunity because non replicating antigen provides transient immune stimulation. Initial dose primes naive B cells in draining lymph nodes producing low affinity IgM and modest IgG, small memory pool, titer often below correlate of protection threshold. Second dose administered 4-8 weeks later triggers anamnestic response with larger germinal center reaction, extensive somatic hypermutation in dark zone mediated by activation induced cytidine deaminase, affinity maturation, isotype class
Ref: Plotkin Why inactivated needs multiple doses; WHO Immunization schedule; Amanna Duration.