A/HRC/7/11 page 14 49. A third implication arising from progressive realization is that at least the present level of enjoyment of the right to the highest attainable standard of health must be maintained. This is sometimes known as the principle of non-retrogression.25 Although rebuttable in certain limited circumstances, there is a strong presumption that measures lowering the present enjoyment of the right to health are impermissible. 50. Finally, progressive realization does not mean that a State is free to choose whatever measures it wishes to take so long as they reflect some degree of progress. A State has a duty to adopt those measures that are most effective, while taking into account resource availability and other human rights considerations. 9. Duties of immediate effect: core obligations 51. Although subject to progressive realization and resource availability, the right to the highest attainable standard of health gives rise to some core obligations of immediate effect. A State has “a core obligation to ensure the satisfaction of, at the very least, minimum essential levels” of the right to the highest attainable standard of health.26 What, more precisely, are these core obligations? Some are discussed later in this report. Briefly, they include an obligation to: (a) Prepare a comprehensive, national plan for the development of the health system; (b) Ensure access to health-related services and facilities on a non-discriminatory basis, especially for disadvantaged individuals, communities and populations; this means, for example, that a State has a core obligation to establish effective outreach programmes for those living in poverty; (c) Ensure the equitable distribution of health-related services and facilities, e.g. a fair balance between rural and urban areas; (d) Establish effective, transparent, accessible and independent mechanisms of accountability in relation to duties arising from the right to the highest attainable standard of health. 52. Also, a State has a core obligation to ensure a minimum “basket” of health-related services and facilities, including essential food to ensure freedom from hunger, basic sanitation and adequate water, essential medicines, immunization against the community’s major infectious diseases, and sexual and reproductive health services including information, family planning, prenatal and post-natal services, and emergency obstetric care. Some States have already identified a minimum “basket” for those within their jurisdiction. Some international 25 Committee on Economic, Social and Cultural Rights general comment No. 14 (2000), para. 32. 26 Ibid., paras. 43-45.