NEW YORK (AP) — Novavax Inc. stock surged Thursday after the company said it is working with the National Institutes of Health to evaluate a potential swine flu vaccine. The Rockville, Md.-based company said its scientists produced a virus-like particle in May. The particle is similar in size and structure to particles of the swine flu, but they don’t have the genes needed to replicate. Novavax developed the particle to provoke an immune response against the swine flu in the human body. Novavax also is working with the Division of Microbiology and Infectious Disease, which is part of the National Institute of Allergy and Infectious Diseases. In a note to clients, Rodman & Renshaw analyst Elemer Piros said he expects human trials of the vaccine to begin in late August, and finish in time for flu season at the end of the year. Piros said the NIH could start stockpiling the vaccine before testing is complete. In afternoon trading, shares of Novavax climbed $1, or 53.5 percent, to $2.87. Trading volume was several times the stock’s daily average. Novavax is the second company to announce in recent weeks that it is working on a swine flu vaccine candidate. On May 21, Vical Inc. said it had started testing a protoype vaccine on animals. Vical is developing the vaccine under an agreement with the U.S. Navy.