The massive task of distributing and administering vaccine for the H1N1 pandemic flu is still being hashed out, but some clarity was offered by federal health officials Wednesday on who should stand in line first for the shots.

Pregnant women, children and people who have certain health conditions are considered the most vulnerable to complications from the new flu virus, and they will be given priority for the shots this fall.

Older people, who are among the hardest hit for seasonal flu, are not on the list. They appear to have some immunity to the new bug, perhaps from exposures to related H1N1 viruses that circulated before 1957.

Prioritizing who gets the new vaccine is necessary given the initial limited supply. By October, the federal government expects to receive about 120 million doses, a fifth of the 600 million doses required to inoculate all Americans with the necessary two-injection vaccine.

Stocks will be divided among the states based on their populations.

Other details -- such as how people prove they are in the high-priority groups for vaccine -- have yet to be worked out.

Already, the virus is widely circulating, which is unusual.

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