Health care workers lined up to be inoculated against swine flu as the United States began a massive campaign to administer 250 million vaccinations by year's end.
"Vaccine efforts are starting. All states in the US have ordered vaccine. It is being delivered," said Thomas Frieden, head of the Centers for Disease Control and Prevention (CDC), the agency leading the charge against H1N1 influenza.
Health care workers, who are among the most at-risk groups according to the CDC, are at the head of the line for the vaccine.
The first H1N1 vaccinations were administered to doctors, nurses, first responders and other health personnel in the states of Illinois, Indiana and Tennessee.
But they got a squirt up the nose, not a shot in the arm, as the nasal spray vaccine has rolled off production lines ahead of the injectable variety.
Just one dose of the nasal spray vaccine provides a robust immune response against H1N1 in adults within eight days, but children under the age of nine, another at-risk group, will likely need two doses.
Some 2.4 million doses of vaccine were available and nearly all have been ordered by public health authorities across the United States, although not all the doses have been delivered, said Frieden.
