Nov. 20, 2009 (United Press International) -- Influenza cases are down in some parts of the United States, but 43 states are still reporting activity, health officials said Friday.

"Even if things do get better and better over the next several weeks, we look at that 1957 experience where after the first of the year, a second wave of mortality occurred," Dr. Anne Schuchat, director of CDC's National Center for Immunization and Respiratory Diseases, told reporters at a briefing in Atlanta.

The latest report of flu cases in 43 states was down from 46.

"I wish I knew if we had hit the peak," Schuchat said. "What I can say is that even when a peak has occurred, half of the people who are going to become ill haven't gotten ill yet."

Overall, about two-thirds of U.S. children (laboratory confirmed) who died from influenza have had an underlying conditions such as asthma or neurological problems like cerebral palsy, and about one-third have not, Schuchat said.

"The children have an influenza virus causing disease and then they get one of these common bacterial infections and it's very severe pneumonia on top. We've seen staph aureus and we've also seen the pneumococcus, but it's a bacteria that we have a good vaccine for, a vaccine that's good in children and high-risk adults," Schuchat said.

Specifically, 54.1 million doses of H1N1 vaccine have become available for the states -- 11 million doses more than we were at a week ago -- about half of the vaccines have gone to children, Schuchat said.