Cases of the H1N1 pandemic flu are still cropping up in the U.S., although most states are now reporting only local or sporadic activity, the CDC said. The exceptions -- at opposite ends of the country -- are Maine and Alaska, where officials are seeing widespread activity, according to Jay Butler, MD, director of the CDC's H1N1 vaccine task force. It's not clear why the flu is more active in those two states, although such variability is common during the annual seasonal flu season, Butler told reporters during a telephone press conference. He said health officials are planning for a "lot of activity" in the fall, expecting both seasonal and H1N1 flu to be present. Five drugmakers are working on H1N1 flu vaccines, he said, and between 45 million and 52 million doses should be available by mid-October. By the end of the year, officials are expecting to have a total of 195 million doses. But important details of the vaccines remain to be worked out, according to Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases. Those details include the dose that will be given -- 15 or 30 micrograms -- and whether one or two doses will be needed. Two clinical trials to study those issues are under way, Fauci said -- one is fully enrolled and the other was expected to be fully enrolled today. Other trials will try answer:- How the vaccine should be given with a seasonal flu vaccine -- before, simultaneously, or after.- How the vaccines will work in children and high-risk groups, such as pregnant women. - How they will work with adjuvants to boost their potency. So far, there have been "no red flags" in terms of safety, Fauci said, although it's too early to say anything about dosing or schedules. The CDC's Butler said there have been 7,963 laboratory-confirmed cases of H1N1 that required inpatient care, and 522 deaths. But those numbers, he said, "radically underestimate" the true numbers because isolates from many cases would not have been tested. In the U.S., the virus continues to strike younger people "disproportionately," Butler said, with 75% of the hospital cases and 60% of the deaths younger than 49. The pattern is similar in the Southern Hemisphere, he said, where by and large H1N1 activity appears to be decreasing. The CDC and international health authorities have been watching our neighbors to the south for signs that the behavior and epidemiology of the virus -- or the virus itself -- has begun to change. "We have not seen those events," Butler said.