The U.S. government said on Friday it is setting aside $1 billion to help companies develop a vaccine against the new strain of H1N1 influenza that is sweeping the world.

U.S. Health and Human Services (HHS) Secretary Kathleen Sebelius said the money will be used for clinical studies over the summer and for commercial-scale production of vaccine ingredients for the government's stockpile of drugs and vaccines that is on hold in case of a pandemic of influenza.

The actions we are taking today will help us be prepared if a vaccine is needed, Sebelius said in a statement.

The companies approved to sell flu shots in the United States are Sanofi-Aventis SA (SASY.PA), Novartis AG (NOVN.VX), GlaxoSmithKline PLC (GSK.L) and CSL Ltd (CSL.AX). AstraZeneca (AZN.L) unit MedImmune also sells a nasal spray flu vaccine.

With these funds manufacturers will also prepare pilot lots of potential vaccine for use in clinical studies to determine the proper dose for a vaccine, determine if adjuvants are appropriate and ensure a vaccine is safe and effective, HHS said in a statement.

Adjuvants are immune system boosters added to vaccines to make them work better. They are used together with killed or weakened versions of the virus to make the vaccine.

The U.S. government will share as much information as possible from the results of these clinical studies with the World Health Organization and the global community so that other countries can benefit from the U.S. efforts to determine dosage, safety and effectiveness, HHS added.

World health experts have not yet decided if a vaccine is needed against the new strain of swine flu, which has infected more than 11,000 people in 42 countries, and killed 86.

On Friday the U.S. Centers for Disease Control and Prevention reported 6,552 probable and confirmed cases of the newly discovered virus, and nine deaths.

The CDC said this likely represents only the tip of the iceberg in the United States, with the true number closer to more than 100,000 cases.

Experts say that a vaccine against the new swine flu virus would probably have to be given separately from the seasonal flu vaccine, which is a mixture of three flu strains reformulated every year. Vaccine makers are almost done with the autumn flu vaccine for the northern hemisphere. (Additional reporting by Lisa Richwine in Washington; Editing by Brian Moss)

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