Which of the following study designs provides the highest level of evidence for assessing the effectiveness of a vaccine in a real-world population after licensure?

• A Phase III double-blind RCT
• B Prospective cohort study (post-marketing surveillance)
• C Ecological study comparing vaccination rates and disease incidence
• D Cluster randomized trial in the target population ✓

Explanation

For real-world population effectiveness, a cluster randomized trial (CRT) in the target population provides the highest level of experimental evidence — randomization occurs at the community level, preserving herd immunity effects that individual RCTs miss. Phase III RCTs assess efficacy under controlled conditions, not effectiveness in real-world heterogeneous populations. Post-marketing cohort studies and ecological studies are observational and rank lower in the evidence hierarchy.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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