Sep. 15, 2009 (United Press International) -- The U.S. Food and Drug Administration announced approval Tuesday of four vaccines to be used against the H1N1 influenza virus, also called swine flu.

The federal agency said the vaccines will be distributed nationally within the next four weeks.

"Today's approval is good news for our nation's response to the 2009 H1N1 influenza virus," said FDA Commissioner Margaret Hamburg. "This vaccine will help protect individuals from serious illness and death from influenza."

The vaccines are manufactured by CSL Limited (OOTC:CMXHY) , MedImmune LLC, Novartis (NYSE:NVS) Vaccines and Diagnostics Limited, and Sanofi Pasteur Inc. All four firms manufacture used the same processes, which have a long record of producing safe seasonal influenza vaccines.

"The H1N1 vaccines approved today undergo the same rigorous FDA manufacturing oversight, product quality testing and lot release procedures that apply to seasonal influenza vaccines," said Dr. Jesse Goodman, the FDA's acting chief scientist.

Based on preliminary data from multiple clinical studies, the H1N1 vaccines induce a robust immune response in most healthy adults eight to 10 days after a single dose, officials said. Clinical studies under way are expected to provide additional information about the optimal dose in children.

Vaccines against three seasonal virus strains are already available, but they do not protect against the 2009 H1N1 virus, the FDA said.