Mexican health authorities on Thursday confirmed 300 swine flu cases and 12 deaths due to the virus among a total of 679 people tested so far. Less than half of the suspected cases tested have been confirmed as swine flu, and a series of visits to the families of victims also turned up relatively few suspected cases. Authorities had previously listed 260 confirmed cases, and said the number of cases appeared to be stabilizing. Health Secretary Jose Cordova said one encouraging sign was that the daily number of people admitted to government-run Social Security hospitals with swine flu symptoms had fallen from a high of 212 people on April 20 to 46 on Thursday. Health workers have so far visited the homes of 77 suspected victims and found only two cases in which relatives tested positive for an A-type flu virus that could be related to the swine strain. Cordova said Thursday that authorities had approved or spent 1.6 billion pesos ($116 million) for medical supplies and equipment so far in the epidemic. Meanwhile, worries about the spread of the virus mounted Thursday in the US as swine flu cases passed 100, and nearly 300 schools closed. Federal officials had to spend much of the day reassuring the public it's still safe to fly and ride public transportation after Vice President Joe Biden said he wouldn't recommend it to his family. Scientists were racing to prepare the key ingredient to make a vaccine against the never-before-seen flu strain - if it's ultimately needed. But it will take several months before the first pilot lots begin required human testing to make the vaccine is safe and effective. If all goes well, broader production could start in the fall. "We think 600 million doses is achievable in a six-month time frame" from that fall start, Health and Human Services Assistant Secretary Craig Vanderwagen told lawmakers Thursday. "I don't want anybody to have false expectations. The science is challenging here," Vanderwagen told reporters. "Production can be done, robust production capacity is there. It's a question of can we get the science worked on the specifics of this vaccine." Until a vaccine is ready, the government has stockpiled anti-viral medications that can ease flu symptoms or help prevent infection. The medicines are proving effective. Reassurances from top health officials didn't stop the questions from coming. An estimated 12,000 people logged onto a Webcast where the government's top emergency officials sought to cut confusion by answering questions straight from the public: Can a factory worker handling parts from Mexico catch the virus? No. Can pets get it? No. And is washing hands or using those alcohol-based hand gels best? Washing well enough is the real issue, answered Dr. Richard Besser, acting chief of the Centers for Disease Control and Prevention. He keeps hand gel in his pocket for between-washings but also suggested that people sing "Happy Birthday" as they wash their hands to make sure they've washed long enough to get rid of germs. Although it is safe to fly, anyone with flu-like symptoms shouldn't be traveling anywhere, unless they need to seek medical care. The swine flu outbreak penetrated over a dozen states and even touched the White House, which disclosed that an aide to Energy Secretary Steven Chu apparently got sick helping arrange President Barack Obama's recent trip to Mexico but that the aide did not fly on Air Force One and never posed a risk to the president. So far US cases are mostly fairly mild with one death, a Mexican toddler who visited Texas with his family. Most of the US cases so far haven't needed a doctor's care, officials said. Still, the US is taking extraordinary precautions - including shipping millions of doses of anti-flu drugs to states in case they're needed. The World Health Organization is warning of an imminent pandemic because scientists cannot predict what a brand-new virus might do. A key concern is whether this spring outbreak will resurge in the fall. The CDC confirmed 109 cases Thursday, and state officials confirm 22 more. Cases now are confirmed in New York, Texas, California, South Carolina, Kansas, Massachusetts, Indiana, Ohio, Arizona, Michigan, Nevada, New Jersey, Delaware, Maine, Colorado, Georgia and Minnesota.