The intended recipient species is the primary determinant: vaccines for use in humans are regulated by FDA's Center for Biologics Evaluation and Research and require a Biologics License. Vaccines intended for use in animals are regulated by USDA APHIS under the Virus-Serum-Toxin Act and require a USDA product license. Some products with dual use may require coordination between both agencies.

Antisera and blood fractions are derived from blood and consist of proteins such as immunoglobulins or clotting factors, while cell therapy products are living cells prepared for therapeutic administration. The distinction matters both for classification and for the applicable regulatory pathway — cell therapies face a more complex FDA review process under the biologics framework, including potential IND and BLA requirements.