The initial swine flu vaccine doses this week will be the nasal spray version, and arm injections will begin next week to help meet demand, health officials said Tuesday.

About 2.2 million doses of nasal spray are available so far. However, the spray is not recommended for some people who are most in danger of complications from flu, including pregnant women and people with asthma. While some priority groups like health care workers and healthy children 2 or older can get vaccinated this week, pregnant women and others at risk should wait.

The vaccine first became available in some states on Monday. So far, demand for it is outstripping supply, said Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, at a Tuesday press conference. He did not say by how much.

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Swine flu is widespread across the country, although cases are on the upswing in some areas and seem to be receding in others, Frieden said.

According to the latest CDC data, reports are falling a bit in five regions that comprise about half the country — the New York-New Jersey area; the Southeast; the Midwest; the central Plains; and the region that includes Hawaii, California, Nevada and Arizona.

However, the unpredictable flu could make a resurgence, Frieden said, noting it's not too late for people in any region to be vaccinated.

"Even in places where flu has been widespread, it's affected 5 percent to 10 percent of the population. That means 90 percent to 95 percent of the population is still susceptible," he said.

The CDC doesn't have an exact count of swine flu deaths and hospitalizations, but existing reports suggest the infection has caused more than 600 deaths and more than 9,000 hospitalizations since the virus was first identified in April.

The government keeps a more careful count of deaths of pregnant women and children attributed to swine flu. CDC officials say they are aware of 28 deaths of pregnant women and about 60 of children.

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On the Net:

U.S. government swine flu Web site: http://www.flu.gov