Here are some facts about influenza:

* Seasonal influenza kills between 250,000 and 500,000 people globally every year, according to the World Health Organization. This includes 36,000 people in the United States alone.

* A new strain of flu could cause a pandemic, a global epidemic that could kills tens of millions of people.

* No one can say where or when this might happen but scientists are very worried about H5N1 flu, currently affecting birds in Asia, the Middle East, Europe and Africa.

* H5N1 rarely infects people but it has killed 254 out of 408 infected since 2003. The fear is it could mutate into a form that people easily transmit to one another, in which case it would spread rapidly.

* Several drugs can fight flu but only if given within a day or two of symptoms beginning. The new antibodies appear to work even three days after infection, the researchers said.

* Gilead Sciences Inc and Roche AG's Tamiflu, as well as Biota and GlaxoSmithKline's Relenza, can prevent infection but the pills must be taken twice daily to do so. A single injection of antibody might provide three weeks of protection, the researchers said.