* Vaccination of general population starts next week
* Second vaccine for pregnant women on order (Adds details, comments from government)
OTTAWA Oct 21 (Reuters) - Canada will be ready to begin H1N1 flu vaccinations next week after the Canadian government approved on Wednesday a H1N1 vaccine made by GlaxoSmithKline Plc (GSK.L) that will be used for most of the population, federal health officials said.
Canada has ordered 50.4 million doses from the company and at least 2 million have already been sent around the country, but regulatory approval was required before they could be used.
The federal government had initially slated the first week of November for the start of the vaccinations, but provincial governments, which are responsible for health care in Canada, will now be able to start the country's largest ever immunization effort whenever they are ready.
"It's our best defence against being infected by this virus and spreading it to others," Dr. David Butler-Jones, Canada's chief public health officer, told a news conference in Ottawa.
The vaccine, called Arepanrix, should be in use next week, he said, with millions more doses sent weekly to provincial governments during the vaccination period. It contains adjuvant, which is a natural product that allows for more effective use of vaccine supplies.
The government in British Columbia, where most of Canada's recent flu outbreak has emerged, said it would begin vaccinations on Monday.
The federal government has also ordered 1.8 million doses of a second vaccine, without adjuvant, specifically for pregnant women. It will be available in early November.
The Canadian government recommends that people at greatest risk should get the vaccine first -- people under 65 with chronic conditions, pregnant women, children six months to five years old, people in remote communities, health care workers and care providers of high-risk persons.
Health officials will largely trust those lining up first for flu shots that they fit one of those criteria, Butler-Jones said.
The virus is different from seasonal flu virus in that it has a strong effect on young people, he said. Teenagers accounted for half of all flu deaths in the United States recently, he said.
Vaccinations are already under way in various countries including the United States, China, Australia. Britain began immunization on Wednesday.
The H1N1 pandemic has killed 83 people in Canada and hospitalized 1,500. Canada has a population of 33.7 million people.
Health Minister Leona Aglukkaq said no decision has been made on whether Canada will share surplus vaccine supplies with other countries. (Reporting by Rod Nickel and Randall Palmer; editing by Peter Galloway)