Gaithersburg-based Novavax Inc. - known for its work developing vaccine candidates for the flu, a pediatric respiratory illness and Ebola - expanded into a new 54,000-square-foot research and development space where it plans to house its vaccine work. "It's a very important signal of our continued growth," said Buck Phillips , chief financial officer of Novavax of the new space at 21 Firstfield Road, across the street from its headquarters.