Did you know that every year millions and millions of eggs are intentionally infected with flu viruses? It's how flu vaccines are made.

Just to be clear, vaccine makers crack the eggshell and inject the virus into the white stuff surrounding the yolk. Then they reseal the egg, the embryo becomes infected, and the virus is allowed to copy itself trillions of times over. They use eggs because eggs are easy to infect and are relatively cheap.

The problem with using eggs to make flu vaccines is that normally there are plenty of eggs to go around, but when there's a sudden outbreak  the eggs can run out pretty fast. That's one of the reasons why researchers are experimenting with a new way to grow flu vaccines.

Instead of infecting eggs, they're trying to grow flu viruses in cultured human and animal cells. When an epidemic occurs, doctors could simply grow a large colony of cells, and then more easily develop enough vaccine.

This method may not only save time, but also potentially produce more effective vaccines. The vaccine grown in cells may be better at mimicking the flu virus that infects people.