The US Food and Drug Administration (FDA) has approved a new 4-strain seasonal flu vaccine from GlaxoSmithKline plc (GSK), the company announced on Monday.

Fluarix Quadrivalent is approved for use in adults, plus children aged 3 and over, to protect them from disease caused by influenza virus subtypes A and B contained in the vaccine.

It is the first intramuscular vaccine to protect against four strains of seasonal influenza virus, says GSK.

The vaccine is not approved or licensed for use in any other country.

Current seasonal flu vaccines help protect against three strains: the two most common A strains in humans and the B strain that scientists think will dominate that year.

This works as long as the B strain selected is the one that actually dominates in the next season.

However, since 2000, two B strains (Victoria and Yamagata) have been dominant to various degrees, increasing the chance that the 3-strain vaccine may not include the right one, as Leonard Friedland, VP and Head of GSK North America Vaccines Clinical Development and Medical Affairs, explains in a statement:

"Trivalent influenza vaccines have helped protect millions of people against flu, but in six of the last 11 flu seasons, the predominant circulating influenza B strain was not the strain that public health authorities selected."

GSK's 4-strain vaccine helps protect against the A strains and both B strains.

The company says Fluarix Quadrivalent will be available in time for the 2013-14 flu season and it also plans to fulfill orders for its 3-strain vaccines.

Health authorities usually place their flu vaccine orders a year before each flu season begins.

The US Centers for Disease Control and Prevention (CDC) recommends adults, and children aged six months and older, get an annual flu shot.

Earlier this month, the CDC said the United States is experiencing the earliest flu season in nearly a decade.

Seasonal flu is estimated to cause 5 million cases of severe illness and nearly half a million deaths worldwide every year.

Click here to see full prescribing information for Fluarix on the FDA website (PDF).

Written by Catharine Paddock PhD