Swine flu is now officially a pandemic, according to the World Health Organization. That's the highest alert level the WHO gives to contagious diseases and the first pandemic declared in 41 years. The raised alert level comes as the city's Health Department confirms today three more deaths due to the H1N1 virus and released estimates yesterday that show 550,000 people could be infected. But, while WHO spokesman Gregory Hartl told Reuters the declaration "doesn't mean anything concerning severity, it is concerning geographic spread," some scientists are painting a graver picture. Said Cambridge University flu virologist Chris Smith to CBS News: "The writing has been on the wall for weeks...WHO probably doesn't want people to panic, but the virus is now unstoppable."

The WHO's pandemic classification could change the way countries shape their public health responses. New quarantine measures, travel restrictions, and trade limits may be imposed along with an increase in money for health services. Drug companies will also be permitted to begin rushed production on an H1N1 vaccine. GlaxoSmithKline says it's already working on a vaccine and could have one ready within six months.

Today's deaths linked to H1N1/swine flu bring the death toll to 15 in New York City. According to the DOH, one victim was under the age of 4, one was between 5 and 24 years old, and the other was between 25 and 54. No other details have been released.