HOUSTON, Dec. 4 (Xinhua) -- The A/H1N1 flu was widespread in only 25 U.S. states last week, mostly in the northeast and southwest, the Centers for Disease Control and Prevention (CDC) said Friday.

    "Twenty-five states reported geographically widespread influenza activity, 17 states reported regional influenza activity, the District of Columbia, Puerto Rico and six states reported local influenza activity, and Guam, the U.S. Virgin Islands and two states reported sporadic influenza activity," the CDC said on its website.

    In late October, 48 U.S. states were reporting widespread A/H1N1 flu activity. But since then, there's been a decline across the country, causing some experts to believe that a fall wave of A/H1N1 flu infections has peaked.

    Meanwhile, "visits to doctors for influenza-like illness (ILI) nationally decreased again this week over last week," the CDC saidi n its latest report, adding that it is the fifth consecutive week of national decreases in ILI after four consecutive weeks of sharp increases.

    The A/H1N1 flu pandemic has so far hit in two waves in the United States. The first wave was in the spring and the second started in the late summer and reached its height at the end of October when the CDC alarmed the nation that 48 states were having widespread flu activities when production delays continued to hamper distribution of the A/H1N1 flu vaccine across the country.

    The remarkable downtrend in the past four weeks has caused some experts to conclude that the second wave of A/H1N1 pandemic had peaked.

    "The peak clearly has passed," said Ira Longini, a statistician at the University of Washington in Seattle who advises the U.S. government on flu.

    Even CDC officials are considering the possibility, but in a more discreet way.

    "We are beginning to see some declines in influenza activity, but there is still a lot of influenza everywhere," said Dr. Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases at the CDC.

    However, flu is hard to predict and some U.S. health officials say they are worried of the possibility of a third wave this winter.

    "We don't know how likely a future wave of A/H1N1 influenza is this year, but we do know that the more people that are vaccinated, the less likely we will have more spread in the coming months," Thomas Frieden, director of the CDC, told a press conference on Friday.

    He advised Americans to get vaccinated, saying that vaccination is the best way to protect people against the new virus and all the data so far on the safety of the vaccine is "reassuring."

Special Report:  World Tackles A/H1N1 Flu