The global eradication of poliomyelitis, a goal set by the World Health Assembly in 1988, may likely be achieved within the next five years. Cases of poliomyelitis have decreased dramatically in the last 20 years, from an estimated 350,000 cases in 1988 to under 1300 in 2004 - a greater than 99% reduction. However, the recent discovery of circulating virulent vaccine derived polioviruses (VDPV), capable of causing paralytic poliomyelitis, threatens eradication. In addition, well-known point mutations of the three Sabin serotypes are associated with development of vaccine-associated paralytic poliomyelitis (VAPP). Thus, global cessation of oral polio vaccine (OPV) use as soon as eradication occurs is a high priority. Understanding the dynamics of circulation of OPV, and especially of VDPV and VAPP, and the impact of human immunodeficiency virus (HIV) infection on viral shedding and on the immunogenicity of inactivated polio vaccine (IPV), is critical for the development of post-eradication vaccination policies. Information about the immunogenicity of IPV regimens is important to assess whether IPV can be used to control potential post-eradication outbreaks in areas of high HIV prevalence. There is a lack of critical data, especially among immunodeficient individuals who may shed more VAPP and VDPV for longer periods than those with normal immune function, to evaluate post-eradication vaccination options being considered by the World Health Organization. We propose to provide data, in a timely fashion, to evaluate the shedding and transmission of OPV, VAPP and VDPV by healthy and immunodeficient populations given OPV in a developing country, and to assess the immunogenicity and mucosal immunity of IPV regimens in healthy and immunodeficient infants living in poor sanitary conditions, which may affect IPV immunogenicity. The proposed studies will be carried among HIV- infected and uninfected infants living in Chitungwiza, Zimbabwe, with an HIV seroprevalence of 20%, to address specific gaps in designing polio vaccination strategies for developing areas of the world. Lay description. Paralytic poliomyelitis (polio) may soon be eradicated. However, polio caused by the live polio vaccine can occur and may threaten efforts to eradicated polio. We propose strategies to identify the effect of HIV infection on polio eradication strategies in a developing country and to study the use of a killed polio vaccine in eradication of poliomyelitis worldwide.