Women with babies joined the thousands of other Torontonians waiting in line at the H1N1 flu clinic at Toronto's Metro Hall on Friday morning. (Robin Rowland/CBC)

The H1N1 vaccine will only be given to Ontarians in priority groups next week due to a temporary shortage of the serum.

Dr. Arlene King, Ontario's chief medical health officer, told a news conference Friday afternoon that the change in plan was precipitated by a lack of doses.

"We will not be immunizing people who do not fall under the six priority groups," she said.

"I strongly encourage persons in these groups to come forward for their immunizations and I would ask people in these groups to go to the nearest flu immunization clinic in their community."

When asked by a reporter whether people who aren't in a priority group will be turned away from clinics, King stressed: "They will not be immunized." She added that "all provinces and territories" will similarly focus on priority groups.

Before Thursday's announcement, the province had earlier simply encouraged healthy adults to stay away from the clinics, but hadn't refused them shots if they showed up.

The province's verification process is counting on people's honesty — those in lineups at clinics will be asked whether they fall into a priority group, King said.

Most regions have vaccination clinics for priority groups between Monday and Friday.

But many regions, including Toronto and the Simcoe Muskoka district, were to open clinics to the general public next week.

The announcement comes as vaccination clinics across Ontario have been inundated with thousands of people, many of whom lined up for hours before clinics opened, only to still be turned away.

"I appreciate that people are losing patience, standing in long lines, and I completely understand why people might be anxious," said King.

"However, if you are a senior or a healthy adult with no medical conditions who doesn't work in a hospital or other health-care setting, where germs are circulating, please wait to get your shot after those who are at greater risk get theirs."

She couldn't say when clinics will admit people who aren't in a priority group, as that "will be dependent on when we get more supply."

Less vaccine than expected

On Thursday, the federal government said less vaccine will be available next week than originally expected.

Ontario will only receive about 170,000 doses next week, King said. The province was expecting around a million doses.

The problem is the manufacturer, GlaxoSmithKline, has a single production line but had to stop producing adjuvanted vaccines to make the unadjuvanted type. Adjuvants are used to boost effectiveness, but have not been tested extensively among pregnant women.

With the production line back to making adjuvanted vaccines, federal officials said, distribution to provinces will be back up in the millions.

The province expects to receive 86,600 doses of unadjuvanted vaccine by the end of next week, King said.

Ontario has distributed 1.4 million doses to local health units in the past week and plans to send out an additional 750,000 doses by the weekend.