What is the function of the 351(a) vs 351(k) designations in biologics regulation?

• A. 351(a): Small-molecule licensing; 351(k): Biosimilars seeking licensure as biosimilar products
• B. 351(a): Traditional biologics licensing; 351(k): Biosimilars seeking licensure as biosimilar products
• C. 351(a): Import licensing; 351(k): Export licensing
• D. 351(a): Vaccines; 351(k): Non-biologics

Answer: (D)

The function of these designations is to identify two different FDA licensing pathways under the Public Health Service Act for biologics. The 351(a) path is used for traditional biologics—the initial licensing route for a new biologic where a full Biologics License Application is evaluated on the product’s own safety, efficacy, and manufacturing data. In contrast, the 351(k) path is for biosimilars seeking licensure as biosimilar products; this route focuses on demonstrating high similarity to a licensed reference product, with no clinically meaningful differences in safety, purity, or potency, and may rely on comparative data and extrapolation to other indications under specified conditions. The distinction is not about vaccines versus non-biologics; vaccines fall under biologics and are governed by the traditional 351(a) pathway for initial licensure, while 351(k) pertains specifically to biosimilar products.