Public health experts are gearing up for swine flu vaccinations this fall in what could be the largest mass-immunization campaign since the polio vaccine was introduced more than 50 years ago. Local public health agencies will bear much of the responsibility for vaccinating the public. For now, there are more questions than answers with regard to flu vaccinations, including how much of the vaccine will be made, when it will available, and who will get it first. In fact, the federal government has not officially announced plans to make a vaccine widely available, although it is expected to do so by the end of summer. There's still a lot of information we have to figure out, and we're learning as we go," said Dr. Mantu Davis, deputy health officer with the Alameda County Public Health Department. "It's definitely a larger vaccination than anything we've seen, or anything in my lifetime." California authorities designed a mass vaccination plan years ago, under the assumption of a deadly pandemic flu and a limited vaccine supply, said Dr. John Talarico with the state public health department's Center for Infectious Disease. That plan is being revised, given that swine flu seems to be fairly mild so far and that a relatively large amount of vaccine may be available, even if it's not enough to give to everyone at once. A swine flu vaccine is still being designed, and the World Health Organization reported last week that a licensed version may not be available until the end of the year - weeks after the start of the flu season. An unlicensed vaccine - one that is still being tested but is deemed safe enough for the general public - may be available sooner.