Army Medical Center (now the Walter Reed Army Institute of Research) from 1948 to 1957, Hilleman discovered the genetic changes that occur when the influenza virus mutates, known as antigenic shift and antigenic drift, which he theorized would mean that a yearly influenza vaccination would be required. In 1957, Hilleman joined Merck & Co. (Kenilworth, New Jersey), as head of its new virus and cell biology research department in West Point, Pennsylvania. It was while with Merck that Hilleman developed most of the forty experimental and licensed animal and human vaccines with which he is credited, working both at the laboratory bench as well as providing scientific leadership. Hilleman served on numerous national and international advisory boards and committees, academic, governmental and private, including the National Institutes of Health's Office of AIDS Research Program Evaluation and the Advisory Committee on Immunization Practices of the National Immunization Program. Asian flu pandemic Hilleman was among the first to recognize that a 1957 outbreak of influenza in Hong Kong could become a huge pandemic. Working on a hunch, after nine 14-hour days he and a colleague found that it was a new strain of flu that could kill millions. Forty million doses of vaccines were prepared and distributed. Although 69,000 Americans died, the pandemic could have resulted in many more deaths in the United States. Hilleman was awarded the Distinguished Service Medal from the American military for his work. His vaccine is believed to have saved hundreds of thousands of lives. In 1968, during the Hong Kong flu pandemic, Hilleman and his team also played a key role in developing a vaccine, and nine million doses became available in 4 months. SV40 Hilleman was one of the early vaccine pioneers to warn about the possibility that simian viruses might contaminate vaccines. The best-known of these viruses became SV40, a viral contaminant of the polio vaccine, whose discovery led to the recall of Salk's vaccine in 1961 and its replacement with Albert Sabin's oral vaccine. The contamination actually occurred in both vaccines at very low levels, but because the oral vaccine was ingested rather than injected, it did not result in infections or any harm. Mumps vaccine In 1963, his daughter Jeryl Lynn came down with the mumps. He cultivated material from her, and used it as the basis of a mumps vaccine. The Jeryl Lynn strain of the mumps vaccine is still used