Bird flu kills more than 60 percent of its human victims, but doesn't easily pass from person to person. Swine flu can be spread with a sneeze or handshake, but kills only a small fraction of the people it infects.
So what happens if they mix?
This is the scenario that has some scientists worried: The two viruses meet — possibly in Asia, where bird flu is endemic — and combine into a new bug that is both highly contagious and lethal and can spread around the world.
So what happens if they mix?
This is the scenario that has some scientists worried: The two viruses meet — possibly in Asia, where bird flu is endemic — and combine into a new bug that is both highly contagious and lethal and can spread around the world.
