Moderna's stock price fell 7% after the FDA declined to review the company's seasonal flu vaccine. The setback comes as a significant blow to the biotech firm's efforts to expand beyond its COVID-19 vaccine business. The FDA's decision means Moderna cannot proceed with regulatory approval for its mRNA-based flu vaccine candidate.

This regulatory rejection represents a major hurdle for Moderna's diversification strategy. The company had been counting on its flu vaccine to become a key revenue driver in the post-pandemic era. Moderna shares dropped sharply in morning trading following the announcement, reflecting investor disappointment with the development.

The FDA's refusal to review the flu vaccine application raises questions about the readiness of Moderna's mRNA technology for broader infectious disease applications. This setback could impact the company's pipeline and future growth prospects beyond COVID-19 vaccines.