Most flu viruses enter human cells through a single entryway — but new research has revealed a "back door" some germs can use to more easily infect cells and jump between species.
Seasonal influenza viruses infect about 1 billion people each year. Typically, these flu viruses enter our cells by binding to sugar molecules, called sialic acids, on the surfaces of cells. This triggers a process that moves the virus into the cell, where it can then replicate.
