Vaccine shortages have been a frequent problem during the past 50 years, but most shortages have been associated with a single product and were of short duration with minimal disruption to national immunization programs. In 2001 attention was directed to the vulnerability of the vaccine supply when, for various reasons, 8 of the 11 vaccines recommended for universal immunization of infants and children were unavailable or in short supply. In addition, tetanus toxoid was in short supply and needed to be prioritized for emergency use only. Although most of these shortages resolved in the following year, periodic shortages of pneumococcal conjugate vaccine (Prevnar; Wyeth Vaccines, Collegeville, PA) continued into 2004. The shortage of trivalent inactivated influenza virus vaccine (TIV) in the fall of 2004 was reported each night on national and local news and was the subject of Congressional inquiries. The legislators wanted to know why this country with vast resources and huge manufacturing capability was unable to provide a reliable supply of routinely recommended vaccines. The immediate answer to the Congressional inquiry about influenza vaccine shortage was the contamination problem at the Chiron plant in Liverpool, England. However, there are substantive problems with domestic vaccine-manufacturing capacity; shortages will likely continue to occur until core problems are addressed. Since 2002, concern about the vulnerability of vaccine production and supply has been the subject of workshops convened by the National Vaccine Advisory Committee (NVAC) of the Department of Health and Human Services,1,2 the focus of a Congressional accounting office report,3 was discussed at a colloquium of the Sabin Institute,4 has been considered by the Institute of Medicine (IOM),5 and is extensively reviewed in a series of articles about development, financing, and implementation of vaccine programs.6 Pediatricians are called on to modify vaccine schedules when … Address correspondence to Jerome O. Klein, MD, Pediatric Infectious Diseases, Finland 5, Boston Medical Center, 774 Albany St, Boston, MA 02118. E-mail: jerome.klein{at}bmc.org