A top World Health Organization official says the H1N1 swine flu virus  is "unstoppable" and says every country needs the vaccine.

WHO vaccine research chief Marie-Paule Kieny said Monday that health care workers should get immunized first because they are needed during an outbreak.

She said authorities must then decide who gets shots next.

Swine flu is mild in healthy people and most victims do not need hospitalization.

But the virus can be severe and even deadly in those with other serious health concerns, including asthma and pregnancy.

Researchers also say that extreme obesity is now considered a risk factor for a severe reaction.

Meanwhile, officials in Britain, Thailand, and the Philippines all reported new swine flu deaths Monday.

The latest WHO report confirms nearly 95,000 swine flu cases around the world, with 429 deaths.

Some information for this report was provided by AFP, AP and Reuters.