Development of pre-pandemic influenza candidate vaccine viruses for use in vaccine manufacturing.

Influenza A viruses continually pose pandemic threats, underscoring the need for timely development of Candidate Vaccine Viruses (CVVs) that meet regulatory expectations for vaccine manufacturing. This protocol describes the procedures used at CDC to generate recombinant CVVs through reverse genetics in accordance with World Health Organization guidelines and CDC's internal Quality System Requirements (QSR)1-3. The QSR incorporates relevant principles from the FDA's Good Manufacturing Practice (GMP) and Good Laboratory Practice (GLP) regulations, providing a structured framework that ensures documentation integrity, material traceability, and quality oversight during all stages of CVV development. The protocol provides detailed steps for plasmid preparation, virus rescue in Vero cells, and amplification in embryonated chicken eggs, and outlines characterization assays used to confirm the suitability and safety attributes of each CVV. This standardized, quality-driven workflow has supported multiple regulatory submissions and facilitated the transition from CVV development to vaccine manufacturing, strengthening pandemic preparedness.