Reader comments
Virologist warns state health workers of swine flu's second wave

The virus (and previous pandemic viruses) has probably not adapted to infect the cells of the lower respiratory tract. Avian flu is adapted to the lungs but not the upper respiratory tract so it is fatal but hard to transmit. When the new flu does adapt to both cell types, It will be able to induce more coughing, shead more virus particles and not have to get all the way into the lungs to infect a new host. Plus it will be much more fatal.