Common flu isn such a big deal. Why are we suddenly being warned about a deadly pandemic?
They won’t like this in Kansas, but it’s all down to evolution. Flu is such a successful virus that each year almost everyone on Earth is exposed, and about a third of us get sick. It is by no means harmless – it kills between 50 and 200 people per million every year, especially the elderly. Flu can kill in several ways. It can destroy your lungs or damage them so much that bacteria run riot and finish the job. Your immune response to the virus can trigger a crisis such as a heart attack or even spiral out of control and kill you. Despite these dangers, most of us fight off a flu virus every year and become immune to that particular strain. But flu keeps coming back. Like all viruses with genes made of RNA, its replication is error-prone, and every infection produces swarms of mutants. Once most people have become immune to the surface proteins on a strain, this virus cannot spread further. Then a mutant offspring, one that is different enough to partly evade the immune reaction direct
