Vaccines are one of the most cost-effective, successful interventions in the history of public health. In the United States, they are financed through an intricate patchwork of public and private funding mechanisms and programs. An important component of vaccine financing is the "safety net" that provides vaccines for individuals who fall through the cracks of the system. State public health agencies rely on this safety net to ensure that children and adults are vaccinated and communities are protected against infectious diseases. However, safety nets need constant maintenance. Small rips or tears weaken the net and, if left untended, can grow into gaping holes. The vaccine safety net has been weakened by neglect and needs repair.Public funding has not kept pace with the cost of vaccinations, causing the safety net to fray. The National Vaccine Advisory Committee (NVAC) appropriately sounds a warning in its report, Assuring Vaccination of Children and Adolescents Without Financial Barriers. 1 The NVAC recommendations to strengthen and to fund fully the existing vaccine safety net programs should be adopted immediately, before we experience serious disease outbreaks.For the majority of children in the United States, cost is not a barrier for vaccinations. Most health insurance plans cover the costs of vaccinations. For children without insurance, the federal government provides free vaccines through the Vaccines for Children (VFC) program. However, ϳ11% of young children and 21% of adolescents fall outside the care of private insurance and government programs, because they are not covered by health insurance and are not eligible for free VFC vaccines. 2 These are the children of working families with health insurance that does not cover immunization, children traditionally covered by vaccines purchased through a federal grant program known as Section 317. These underinsured children are most in need of the safety net offered by state and local public health departments. Many public health officials are concerned that, with worsening economic conditions, the number of children who depend on this safety net for their vaccines will increase beyond the ability to support the demand.Historically, state and local public health departments, through a combination of state and Section 317 federal grant funds, have been able to provide vaccines for underinsured children and adults. This safety net of coverage has kept overall immunization coverage rates high and ensured widespread community protection against outbreaks of vaccine-preventable diseases. New, more-expensive vaccines have taxed the system, however, and challenging economic times have forced many states to cut back on vaccine purchases because of lack of state or federal funding. Twenty-four states are unable to provide vaccines for underinsured children in the private sector. 3 At least 13 states have changed their policies regarding provision of publicly purchased vaccines since 2004 and now restrict access to selected vaccines. 4 Although national immunizat...