A universal flu vaccine could be available as soon as 2014, if scientists have their way.

That goal has eluded researchers for years, because different strains of the flu virus circulate each season, forcing scientists to predict upcoming strains and patients to get a new vaccine every fall.

The efficacy of the vaccine varies from year to year, but it is usually between 30 and 60 percent effective, because there is no way to identify all possible strains, and because the strains that are prevalent when the vaccines are manufactured won't necessarily be prevalent when flu season rolls around.

A universal flu vaccine would train the immune system to recognize the basic elements that are common to all strains of the flu, which would give a higher protection rate and allow one vaccine to last for several years.

The influenza virus is studded with nail-shaped proteins, called hemagglutinin, the Los Angeles Times explained. The heads of those nails are flashy and constantly morphing. They distract the immune system and prevent it from seeing the less variable flu parts underneath, which might allow the body to recognize more than one kind of flu. Inside the virus are other variable proteins that disguise infected cells. The immune system tends to focus on these ever-changing parts.

One company, BiondVax Pharmaceuticals in Ness Ziona, Israel, is working on a vaccine that it says could be ready for approval by the Food and Drug Administration by 2014, and a London-based pharmaceutical company, Seek, is aiming to get its own vaccine out within five years.

Other researchers say a universal flu vaccine will take 10 years -- but they agree it is on the horizon.

The need for a universal flu vaccine is becoming increasingly urgent as new, deadlier flu strains emerge. In 2009, the H1N1 strain, or swine flu, caused widespread panic, and this summer, the World Health Organization announced a resurgence of H5N1, or bird flu, in Asia.

The H5N1 strain remains uncommon because it has not yet mutated into a form that can spread directly from person to person, but it is remarkably serious in people who do get it, with a fatality rate of nearly 60 percent.

With so many new and old strains circulating, it is virtually certain that one of them will develop the capacity to threaten lives on a global scale.

It's almost inevitable that another pandemic will come, Antonio Lanzavecchia, an immunologist at the Swiss Federal Institute of Technology in Zurich, told the Los Angeles Times.

Scientists are working overtime to ensure that a universal flu vaccine will be available before that pandemic happens.