The U.S. government's $6.4 billion swine flu vaccination program is likely to put the American public health sector under unprecedented strain and expose serious shortcomings, Reuters quoted experts as saying. As the first mass U.S. immunization program in a generation ramps up to deliver tens of millions of doses each week, public health experts disagree about how well the country's network of state and local health departments might perform. But many say the sector never received the money it needed for large-scale immunizations despite years of planning for pandemics after the reemergence of bird flu in Hong Kong and South Korea in 2003. "The worst-case scenario is that there is vaccine in a particular state or locale but that state or locale hasn't sufficiently planned to distribute it," said Leonard Marcus of the Harvard School of Public Health. Marcus, who studied the 2005 Hurricane Katrina disaster, said the H1N1 immunization program could encounter similar breakdowns in leadership and coordination wherever local public health systems are underfunded or poorly managed. "Some bureaucrat is going to say he doesn't have authority or needs a signature and it's going to stop the system from moving. That could very well cause panic," he said in a telephone interview. Experts give the Obama administration high marks for creating a program capable of procuring 250 million doses and distributing them to 90,000 sites nationwide so that every American who wants the vaccine can get it. The government has ordered vaccine from five companies -- Sanofi-Aventis SA, CSL Ltd, Novartis AG, GlaxoSmithKline and the AstraZeneca unit MedImmune.