With the world already grappling with a pandemic of 2009 H1N1 influenza, no treatment was more hotly anticipated or more in demand in the U.S. (and the rest of the northern hemisphere) than the new H1N1 vaccine when flu season officially kicked off in the fall. Despite the fact that the vaccine had proved effective in trials with one dose — rather than two, as researchers had originally expected — the vaccine supply from U.S. manufacturers still couldn't keep pace with demand in the first weeks of October, when the first million or so shots rolled off production lines. In many places around the country, there was not enough vaccine even to cover members of priority groups targeted by the government, including young children, pregnant women, health care workers, parents of infants younger than 6 months and those with underlying conditions such as asthma or diabetes. And yet according to the latest polls, 55% of Americans said they would not get the new vaccine — which was created and tested in record time after H1N1 first appeared last spring — because of worries about its safety.