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Flu shots can be hard to sell to the public. Even a run-of-the-mill influenza infection can be debilitating to otherwise healthy people, and lethal to those who are elderly or frail, so vaccinations are important. The problem is that flu vaccines deliver inconsistent performance. “In a good season, we’re up to 60% effectiveness, but in bad, mismatched years it can be as low as 10% or 20%,” says Barney Graham, deputy director of the Vaccine Research Center at the US National Institute of Allergy and Infectious Diseases (NIAID) in Bethesda, Maryland.