A whistleblower suit against Merck, filed back in 2010 by two former employees, [accused] the drugmaker of overstating the effectiveness of its mumps, measles, and rubella vaccine. The scientists claim Merck defrauded the U.S. government by causing it to purchase an estimated four million doses of mislabeled and misbranded MMR vaccine per year for at least a decade, and helped ignite two recent mumps outbreaks that the allegedly ineffective vaccine was intended to prevent in the first place. As the single largest purchaser of childhood vaccines (accounting for more than 50 percent of all vaccine purchasers), the United States is by far the largest financial victim of Merck's fraud. Specifically, the suit claims Merck manipulated the results of clinical trials beginning in the late 1990s so as to be able to report that the combined mumps vaccine ... is 95 percent effective, in an effort to maintain its exclusive license to manufacture it. However, instead of reformulating the vaccine whose declining efficacy Merck itself has acknowledged, the company reportedly launched a complicated scheme to adjust its testing technique so that it would yield the desired potency results. While the Justice Department has refused to rule on the case after conducting its own two-year investigation, the allegations ... offer an extremely damaging view into the inner process of a company accused of misleading both regulators and consumers about a vital medical product.