The Food and Drug Administration on Tuesday approved a vaccine for the pandemic H1N1 influenza from four manufacturers, clearing the way for the vaccine to be administered as soon as enough of it is available.

The approval was announced to Congress by Health and Human Services Secretary Kathleen Sebelius.

The licensing means that the vaccine is made properly and meets manufacturing and quality standards. Officials from the National Institute of Allergy and Infectious Diseases announced Friday that the vaccine was safe and produced adequate immunity with only one dose. Researchers had feared that two doses would be required, limiting the amount of vaccine available and complicating the logistics for delivering it.

The United States has ordered enough vaccine for 195 million doses, meaning that “we will have enough vaccine available for everyone,” Sebelius said.

About 45 million doses are expected to be available by the middle of October, and officials are targeting those in the highest-risk groups – primarily pregnant women and health care workers.

In a normal year, about half the people who should receive the seasonal flu vaccine actually get it, and it seems likely that despite widespread publicity campaigns, the turnout for the swine flue vaccine will not be much higher. Many people fear the vaccine because of its supposed “experimental” nature and perceived safety issues, but government scientists say that it is virtually identical to the seasonal flu vaccine, which has been given safely to hundreds of millions of people.

The vaccines approved Tuesday are made by Australia’s CSL Ltd., Switzerland’s Novartis, France’s Sanofi Pasteur and Maryland’s MedImmune, which makes an inhalable vaccine that might be available by the end of the month.