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.
    About 174.5 million doses of the flu vaccine were distributed across the US this flu season through the end of February, of which an estimated 82% were egg-based, according to the Centers for Disease Control and Prevention (CDC).
    With each egg producing one vaccine, that means the US might have used 140 million eggs this flu season alone.
    To prepare for annual flu seasons, as well as possible pandemics, the US government has invested tens or hundreds of millions of dollars over the past 15 years to ensure there are enough eggs for vaccines.
    But now the world faces a new crisis: