1. The virus had a high mortality rate (above 70%). Viruses can't be treated with antibiotics (as plague could be, for instance). Vaccines are dicey, even if we developed one.
2. Smuggled chicken has recently been found in the U.S.
http://msnbc.msn.com/id/7089156/3. According to WHO, this flu could become much more transmissible if it infected someone who was simultaneously infected with human influenza, and the virus picked up human influenza genes. See the WHO report:
http://www.who.int/csr/disease/avian_influenza/enWe have had a late flu season with many people unvaccinated or vaccinated late.
It especially concerns me that an alarm has not been raised more loudly, warning about imported chicken, for instance. It's great that the media reported it, but the public really needs to understand how serious this could be.
Edit: Corrected mortality rate.