The World Health Organization (WHO) declared influenza pandemic on Thursday and called on flu vaccine manufacturers to make enough shots to protect people against flu pandemic.

As of June 11, nearly 30,000 confirmed cases have been reported in 74 countries. The virus is contagious and spreading easily from one person to another.

I have decided today to raise the level of influenza pandemic alert from Phase 5 to Phase 6,WHO Director General Dr.Margaret Chan said in a statement.

The world is now at the start of the 2009 influenza pandemic, she said.

Leading companies are already under way to make billions of shots. Wayne Pisano, head of vaccines at Sanofi-Aventis, the world's largest flu vaccine supplier said that his company would produce the largest number of doses of vaccine in the shortest time frame.

Drug companies have already secured some large orders for H1N1 vaccine from governments in Europe and North America, and fresh ones are expected since the WHO has declared H1N1 a full-blown Phase 6 pandemic.

Dr. Chan said there would be no H1N1 vaccine ready before September but she noted that the virus, which causes only mild disease in most people, was so far proving fairly stable.

The WHO has estimated vaccine makers could produce up to 4.9 billion pandemic flu shots a year in the best-case scenario, though this will still not be enough for the entire world population of more than 6.5 billion, particularly if it turns out that people need more than one injection to gain immunity.

That helped lift shares in Glaxo, Sanofi and Novartis by between 2 and 4.5 percent in New York trade on Thursday.