An increasing number of Americans were concerned over H1N1 flu that was expected to launch the second wave this fall, according to a poll released on Wednesday.

The survey conducted by CNN and Opinion Research Corporation found that 39 percent of people polled said they were worried about the new type of flu virus, almost doubling the 17 percent in May.

About 17 percent of Americans said that they were concerned before but not anymore, while 44 percent said that they have been never worried, said the poll.

The survey was released one day after President Barack Obama called on the nation to be on alert against the second wave of H1N1 flu, which has hospitalized thousands of Americans starting April.

The U.S. government also issued a report on Tuesday, titled 2009-H1N1 National Preparedness and Response Overview, including some key elements of preparedness and response efforts for the fall wave of H1N1 flu.

The report sets four pillars of surveillance, mitigation, vaccine, and communications to respond to potential return of the flu, and requires partnership of Congress, governments at all levels, the medical community, private-sector entities, and community-based groups in these efforts.

It also encourages Americans to "act on a shared responsibility to reduce the impact of H1N1 flu."

According to the Wednesday poll, 59 percent of Americans are confident in the federal government's efforts to prevent a nationwide epidemic, while 40 percent not optimistic.

Tow-thirds of interviewees said that they wanted to get a H1N1 flu vaccine shot after it becomes available, it added.

Official statistics show that during its first wave in the U.S. in April, the H1N1 flu has hospitalized 8,843 and killed 556.

(Xinhua News Agency September 3, 2009)