The supply of H1N1 vaccine is becoming more of a concern for provincial health officials as they respond to strong public demand and peaking flu activity.

Dr. Arlene King, the province's chief medical officer of health, and Health Minister Deb Matthews acknowledged yesterday the number of Ontarians lining up for a shot in the arm far exceeded expectations.

"We are using the vaccine with the existing manpower that we have as fast as we get it," King said. "We are experiencing more demand than we had planned for, clearly."

With word from federal officials that the vaccine supply may not flow as anticipated next week, public health officials are yet again urging healthy Ontarians to wait their turn while priority groups, such as pregnant women, children under five years old and people with chronic conditions, get their inoculations.

"In time, we will have enough vaccine to immunize everyone who needs and wants it," King said.

Despite the deaths of two children, aged 10 and 13, in Ontario, King said children under the age of five are generally at greater risk of needing hospitalization than older children and should get the vaccine first.

Flu activity in the province is now reflecting the peak rates experienced during the height of the spring H1N1 outbreak.

The province has distributed 1.4 million doses of H1N1 vaccine to local public health units and is sending another 750,000 doses by the end of the weekend.