WHO: Swine Flu Now A Pandemic, 1st In 41 Years

Pascal Barollier, a spokesman for Sanofi-Aventis, said they were also working on a pandemic vaccine but WHO had not yet asked them to start making mass quantities of it.

WHO described the pandemic as "moderate." Fukuda said people should not get overly anxious about the virus. "Understand it, put it in context, and then you get on with things," he said.

Still, about half of the people who have died from swine flu were previously young and healthy — people who are not usually susceptible to flu. Swine flu is also crowding out regular flu viruses. Both features are typical of pandemic flu viruses.

Swine flu is also continuing to spread during the start of summer in the northern hemisphere. Normally, flu viruses disappear with warm weather, but swine flu is proving to be resilient.

"What this declaration does do is remind the world that flu viruses like H1N1 need to be taken seriously," said U.S. Secretary of Health and Human Services Kathleen Sebelius, warning that more cases could crop up in the fall.

Now that a pandemic has been declared, some countries might be prompted to devote more money to containing the virus. Many developed countries have pandemic preparedness plans that link spending to a WHO declaration.