The vaccine was shown to be 78 percent effective. The drug was taken in three shots administered over the course of a year. Some uncertainty remained about the vaccine's ultimate safety before it was released to the public, especially for people with certain conditions. When the National Vaccine Advisory Committee of the Food and Drug Administration (FDA) certified the drug in December 1998, members appended a list of concerns about the long-term effect of the vaccine. The FDA released the vaccine on public health grounds, recommending that it be considered by people at the highest risk. GSK took the drug off the market in 2002 for commercial reasons, citing poor sales (with predictions of less than 10,000 people to be vaccinated in 2002), the high price of the vaccine, the need to exclude children under 15, and the need for frequent boosters. Vaccine expert Stanley Plotkin predicted that the withdrawal meant there will never be another Lyme disease vaccine available.