US drug regulators approved a swine flu vaccine on Tuesday, keeping officials on track to begin a mass vaccination campaign by next month, Health Secretary Kathleen Sebelius said.
"I am pleased to report that today, the Food and Drug Administration (FDA) has approved applications for vaccine for the 2009 H1N1 virus for four of the (five) manufacturers of the US licensed seasonal influenza vaccine," Sebelius told US lawmakers.
FDA Commissioner Margaret Hamburg welcomed the approval in a statement.
"Today's approval is good news for our nation's response to the 2009 H1N1 influenza virus," she said. "This vaccine will help protect individuals from serious illness and death from influenza."
The vaccine treatments are produced by CSL Limited, MedImmune LLC, Novartis Vaccines and Diagnostics Limited, and Sanofi Pasteur Inc, and the FDA said all four firms use the same processes.
The US government has purchased 195 million doses of swine flu vaccine and will make shots against the influenza A(H1N1) virus available free of charge starting next month, Sebelius said, although providers might charge a fee to administer them.
"The large-scale 2009 H1N1 vaccine program will begin mid-October with small amounts of vaccine becoming available the first week of October," she said.
The fifth US manufacturer was also expected to be licensed, she added.
Preliminary data from clinical studies showed the approved vaccines "induce a robust immune response in most healthy adults eight to 10 days after a single dose," the FDA said, noting that clinical studies underway would determine the best dose for children.
Vaccination will be on a voluntary basis, with priority given to five groups deemed to be at particular risk from the novel swine flu virus.
The US Centers for Disease Control and Prevention (CDC) has recommended that pregnant women, people in contact with infants, medical personnel, people aged six months to 24 years and adults under the age of 65 with underlying medical conditions should be the first to get the shots.
That is about 160 million people in the United States, less than the 195 million doses of vaccine purchased by the government, only about one third of which are expected to be ready by October.
The vaccine will be available as either a flu shot made with dead A(H1N1) virus, or as a nasal spray made with live, weakened virus, Sebelius said.
Clinical trials are underway to determine if there is "any harm" in having a seasonal flu vaccine, which is already available, at the same time as the vaccine against influenza A(H1N1), Sebelius said.