Question

Which is incorrect for attenuated vaccines?

• A. They require only single booster
• B. They are less stable
• C. They induce only humoral immunity
• D. Sabin is an attenuated Polio vaccine

Hint:

Live Attenuated Vaccines = Replicate inside host cells $\to$ Activate BOTH Humoral (Antibodies) and Cell-Mediated (CD8$^+$ T-cell) Immunity!
Killed/Ictivated Vaccines = Elicit mainly Humoral immunity.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to identify the statement that is false regarding the immunological and biological properties of live-attenuated vaccines.

Step 2: Key Formula or Approach:
Live-attenuated vaccines contain weakened pathogens capable of replicating inside host cells without causing disease. Because they infect cells turally, they present antigens via both MHC Class I and MHC Class II pathways.

Step 3: Detailed Explation:

• Dual Immune Activation (Humoral and Cell-Mediated): Live-attenuated microbes replicate intracellularly inside host cells. Antigenic peptides are processed and presented on MHC Class I molecules to CD8$^+$ Cytotoxic T Lymphocytes (CTLs), stimulating robust cell-mediated immunity. Simultaneously, extracellular viral/bacterial antigens are presented on MHC Class II molecules to CD4$^+$ Helper T cells, driving B cell activation and humoral immunity. Therefore, claiming they induce *only* humoral immunity is incorrect.

• Alysis of True Statements:
• Booster Requirement: Due to transient replication in the host, live-attenuated vaccines provide strong immunogenic stimulation requiring fewer doses or single boosters compared to ictivated vaccines.

• Stability: Live organisms are heat-sensitive and less stable, requiring strict cold-chain storage.

• Sabin Vaccine: The Sabin oral polio vaccine (OPV) consists of live-attenuated poliovirus strains.

Step 4: Fil Answer:
The statement that attenuated vaccines induce *only* humoral immunity is incorrect because they elicit both strong humoral and cell-mediated immune responses.