A 6-month-old infant receives the first dose of live attenuated measles vaccine but fails to seroconvert. The most likely explanation for this vaccine failure is:

• A Immaturity of the infant's dendritic cells at 6 months of age
• B Inadequate cold chain storage destroying the live virus
• C Exclusive breastfeeding interfering with vaccine antigen uptake
• D Maternal IgG antibodies neutralizing the vaccine virus before replication ✓

Explanation

Maternal IgG antibodies transferred transplacentally persist in the infant circulation and neutralize live attenuated vaccine viruses before they can replicate sufficiently to trigger an immune response. This is why measles vaccine is given at 9 months or later under UIP, when maternal antibody titres have declined. This principle applies to other live vaccines like rotavirus and varicella as well.

Reference: Plotkin's Vaccines, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.