This is a multi-center, open-label, long-term study of subcutaneously (SC) administered mepolizumab 100mg in addition to standard of care (SOC), in subjects with severe eosinophilic asthma. This study will enroll a subset of subjects from Study MEA115661 who have demonstrated clear benefit from therapy and who without continuation of mepolizumab therapy are individuals at greatest risk of serious deterioration of their health status. In order to target individuals at greatest risk for serious deterioration of their health status, only subjects from the MEA115661 study with a history of life-threatening or seriously debilitating asthma, will be allowed to participate. Subjects meeting all of the eligibility criteria for the study will be offered the opportunity to consent for this study of up to 128 weeks in length (including the Follow-Up Visit). This study will give opportunity to extend the collection of clinical data for long-term use and further assess the sustainability of efficacy in a population likely to experience significant loss of asthma control and the need for higher doses of systemic steroids if returned to SOC only.