Poliovirus eradication – nature of the oral vaccine: In global immunization programs, the oral polio vaccine (Sabin) consists of which type of poliovirus preparation?

Introduction / Context:
Polio eradication campaigns historically used two vaccines: oral polio vaccine (OPV, Sabin) and inactivated polio vaccine (IPV, Salk). Recognizing their composition and route is essential for understanding mucosal immunity and epidemiology of vaccine-derived strains.

Given Data / Assumptions:

• Three poliovirus serotypes historically circulated (types 1–3).
• OPV is administered orally; IPV is injected.
• Live attenuation enables replication in gut with minimal neurovirulence.

Concept / Approach:
Sabin OPV contains live attenuated strains representing all three serotypes, inducing strong intestinal IgA responses that interrupt fecal-oral transmission. This contrasts with IPV, which is formalin-inactivated and delivered intramuscularly, producing robust serum IgG but less mucosal immunity.

Step-by-Step Solution:
Recall OPV composition: live attenuated serotypes 1, 2, and 3 (historically trivalent; currently strategies may use bivalent/monovalent depending on campaigns).Exclude killed/inactivated options which describe IPV.Select the live attenuated option.

Verification / Alternative check:
Epidemiological data show OPV’s ability to induce herd immunity via secondary spread in communities, consistent with a live attenuated formulation.

Why Other Options Are Wrong:

• Heat-killed/formalin-inactivated: describe IPV, not OPV.
• Wild-type live virus: unsafe and not used for vaccination.
• Subunit only: not the standard licensed polio vaccines.

Common Pitfalls:
Mixing up OPV and IPV properties; assuming oral vaccines are always inactivated.

Final Answer:
Live attenuated strains of all three immunological types.