The bird flu vaccine is made with eggs. That has scientists worried.

Even a peep of news about a new flu pandemic is enough to set scientists clucking about eggs.

They worried about them in 2005, and in 2009, and they're worrying now. That's because millions of fertilized hen eggs are still the main ingredient in making vaccines that, hopefully, will protect people against the outbreak of a new flu strain.

"It's almost comical to be using a 1940s technology for a 21st-century pandemic," said Rick Bright, who led the Health and Human Services Department's Biomedical Advanced Research and Development Authority during the Trump administration.