The US keeps millions of chickens in secret farms to make flu vaccines. But their eggs won't work for coronavirus

(CNN)Across the United States, prized chickens are laying life-saving eggs at secret farms.

Few people know where the chickens are kept -- their locations are undisclosed as a matter of national security.
Each day, hundreds of thousands of their eggs are trucked to facilities, where they are protected by guards and multimillion-dollar, government-funded security systems.
    But these eggs aren't for breakfast; they're the source of your common flu shot.
    For the past 80 years, much of the world has relied on chicken eggs for the production of influenza vaccines.