NEW YORK — The flu vaccine is doing a poor job protecting older Americans and others against the bug that's causing most illnesses.Preliminary figures released Thursday suggest the vaccine is 36 percent effective overall in preventing flu illness severe enough to send a patient to the doctor's office.There's only been one other time in the last decade when the flu vaccine did a worse job.Most illnesses this winter have been caused by a nasty kind of flu called Type A H3N2. The vaccine was only 25 percent effective against that type.This kind of virus tends to cause more suffering and have been responsible for the worst recent flu seasons. But experts have wondered whether low vaccine effectiveness is another reason for the surprisingly severe season hitting the United States this winter.Based on these numbers, the answer is yes."The fact that the vaccine doesn't work as well as we would like is clearly a contributing factor," said Dr. William Schaffner, a Vanderbilt University vaccine expert.The estimates were published by the Centers for Disease Control and Prevention.The numbers are a snapshot taken in the middle of a frantic flu season.