U.S. health officials have approved vaccines from four drugmakers to help prevent the H1N1swine flu, ensuring there will be enough to inoculate Americans who want the protection, U.S. Health Secretary Kathleen Sebelius told lawmakers on Tuesday.

The U.S. Food and Drug Administration cleared vaccines from Sanofi-Aventis SA, CSL Ltd, Medimmune and Novartis AG for the H1N1 strain of influenza, she said.

There will be vaccines for everyone, Sebelius said at a hearing of the U.S. House of Representatives Energy and Commerce Committee.

There are about 300 million potential users, she said, adding that not all Americans will opt for the shot. The first doses should be available within the next four weeks, according to the FDA.

Manufacturers and governments have been scrambling for vaccines to target the new H1N1 flu strain, which was declared a pandemic in June. The World Health Organization said it could infect as many as one-third of the world's population, or 2 billion people.

Sebelius said the government has already contracted to buy 195 million doses from a total of five manufacturers and that more purchases are likely depending on how many people decide to get vaccinated.

GlaxoSmithKline Plc is also working to develop a H1N1 vaccine and win FDA approval.

Some skeptics have questioned the safety of the vaccines, especially given the quick development. Clinical trials for most adults began in early August.

So far, preliminary data show most healthy adults have a good immune response eight to 10 days after receiving a single shot, the FDA said. Other studies are underway for children, and trials for pregnant women just began, Sebelius said.

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, Dr. Jesse Goodman, FDA's acting chief scientist, said in a statement.

FREE VACCINES

U.S. officials are launching a large-scale vaccination effort in mid-October to inoculate the population, including those most at risk such as pregnant women and young people ages 6 months to 24 years.

H1N1 vaccines will be free, Sebelius said, but some healthcare providers may charge an administration fee. The federal government is planning to spend about $1.4 billion for states and hospitals to prepare for the virus, she added.

Flu season typically runs from October to May, but U.S. officials sawH1N1 cases throughout the summer with an uptick from summer camps and now schools.

Still, people won't be able to get the vaccine for weeks.

The fact that vaccines won't begin distribution until October makes preventing the spread of flu even more critical, Sebelius said in her testimony.

Medicine