St. Louis ? As flu vaccine makes its way across the United States, health officials are urging most healthy people to wait until Oct. 24 or after to roll up their sleeves.

Officials say up to a million doses of vaccine should be available this flu season, enough to meet demand, but some uncertainty about the supply remains. Unexpected production problems led to either nationwide delays or shortages in three of the last five years.

“In all honesty, you don’t know how much vaccine you have until the FDA approves it,” said Sue Denny, public information coordinator for immunization programs for the Missouri Department of Health. “Not all vaccine becomes available at the same time. Lots are approved as they are ready.”

Karen McMahon, chief of immunization for the Illinois Department of Public Health, said there haven’t been any red flags yet. “But at any given time, as companies are having lots released by FDA, something could be found,” she said.