(CNN) -- As flu season rages across the United States, federal regulators say they have approved a new kind of vaccine for the virus.
The new product, Flublok, which is available in limited supplies for the current season, is different from other flu vaccines, because it isn't made using eggs or an influenza virus, the Food and Drug Administration said Wednesday.
Instead, Flublok's production involves programming insect cells grown in steel tanks to produce large amounts of a particular flu virus protein, known as hemagglutinin, according to Protein Sciences, the vaccine's manufacturer.
Most human antibodies that fight flu infection are directed against hemagglutinin, the FDA said.
This method allows for more rapid production, making more of the vaccine available more quickly in the event of a pandemic, the FDA said.
"This approval represents a technological advance in the manufacturing of an influenza vaccine," said Karen Midthun, director of the FDA's Center for Biologics Evaluation and Research.
It has already been used in vaccines approved for other infectious diseases.
Flublok is approved only for adults ages 18 - 49.
Flu activity is "elevated" in most of the United States, Dr. Thomas Frieden, director of the Centers for Disease Control and Prevention, said last week.
Manufacturers said there was plenty of vaccine for those who want to get a flu shot. But there have been reports of spot shortages, Frieden said.
Flublok will be available in limited supply this winter and widely available during the next flu season, said Protein Sciences, which is based in Meriden, Connecticut.
Flublok contains the elements necessary to help fend off three different flu strains, including H1N1 and H3N2, the regulator said.
And it proved 44.6% effective against all influenza strains in circulation, not just those that matched the strains included in the vaccine, according to the FDA.