Each year, infection with Human Papillomavirus (HPV) leads to millions of abnormal Pap smears and thousands of cases of cervical cancer in the US. Throughout the developing world, where Pap smears are less common, HPV is a leading cause of cancer death among women. So when the international pharmaceutical giant Merck developed a vaccine that could prevent infection with several key strains of HPV, the public health community was anxious to celebrate a major advance. But then marketing and lobbying got in the way. Merck chose to pursue an aggressive lobbying campaign, trying to make its new vaccine mandatory for young girls. The campaign stoked public mistrust about how vaccines come to be mandated, and now it's not just Merck's public image that has taken a hit. The public health community has also been affected. What is the lesson to be learned from this story? Public health communication relies on public trust.