The annual flu vaccine is the best way to prevent yourself and others from getting sick. But sometimes the antigens the vaccine trains your body to fight are not similar enough to the strains of influenza circulating that year. This mismatch allows viruses to fly under the radar and spread undetected. It's a problem scientists hope to solve with a universal flu vaccine. Dr. Matthew Memoli is an influenza expert at the National Institute of Allergy and Infectious Diseases (NIAID). He is preparing to test a new vaccine candidate that could offer protection from more flu strains and for more people.