Most common cause of vaccine failure

Primary Vaccine failure Failure to serological respond to Vaccine. To young age where maternal antibodies interfere (MC cause) Vaccine production problems Cold chain failure. Inappropriate administration technique Immunodeficiency Poor heath. Secondary vaccination failure "waning immunity" where there is loss of vaccine induced protection in an individual who had previously seroconveed to vaccination Causes are not well understood Ref: Microbiology and Infectious Disease by Hagan & Brunner, 8th edition Pgno : 510