Despite the fizzling swine flu threat, the Obama administration is weighing a fall vaccine campaign that would ask Americans to get two new swine flu vaccines in addition to the seasonal flu shot. The multibillion-dollar effort would challenge vaccine manufacturers as well as the ability of the government to track side effects to the new vaccines. During the 1976 swine flu scare, hundreds of Americans were left with neurological disorders after receiving the voluntary vaccine. “There will be adverse effects to any vaccine. That’s just science,” says Michael Hattwick, who was in charge of tracking vaccine side effects during the ’76 swine flu outbreak. The vaccine would first be tested on animals and then on humans in clinical trials before being rolled out.