A flu vaccine made by a new, faster method works just as well as existing products, researchers reported Tuesday. The finding clears a hurdle in the government's effort to move toward a manufacturing process that could allow for a more reliable supply of seasonal flu shots and quicker responses to pandemics. The new vaccine, which could become available in the United States in the next few years, is made by growing the influenza virus in cultures of animal cells rather than in the chicken eggs that have been used for more than half a century. Using animal cells could shave weeks off the six months or so that is now required to produce a vaccine for a pandemic. In the 2009 swine flu pandemic, large quantities of vaccine were not ready until after the wave of disease appeared to have crested.