What role does viral re-assortment play in flu pandemics?. Earth & Marine Sciences

When two viral strains infect the same cell, their genetic material can become mixed as copies of heir RNA are bundled into new virus particles. The new combinations of genetic material can give rise to new beneficial characteristics of the virus, for example, characteristics that permit bird flus to invade human cells. Humans who have never been exposed to the characteristics of bird flus may have no antibodies to fight the infection, and the virus can reproduce rapidly. A bird flu virus that gains the capacity to spread from human to human through reassortment may spread rapidly over large geographic areas, leading to a serious pandemic.