U.S. travel restrictions implemented in recent days to keep a fast-moving virus that has crippled much of China from spreading across America won't work, top-epidemiologist told U.S.-lawmakers. "I have never seen instances where that has worked when we are talking about a virus at this scale," epidemiologist Jennifer Nuzzo, a senior scholar at Johns Hopkins University's Center for Health-Security, testified before the House-Foreign-Affairs subcommittee.