Global health is the health of populations in a global context and transcends the perspectives and concerns of individual nations. Health problems that transcend national borders or have a global political and economic impact, are often emphasized. Thus, global health is about worldwide improvement of health, reduction of disparities, and protection against global threats that disregard national borders.
The major international agency for health is the World Health Organization (WHO). Other important agencies with impact on global health activities include UNICEF, World Food Program (WFP) and the World Bank. A major initiative for improved global health is the United Nations Millennium Declaration and the globally endorsed Millennium Development Goals.
In 1948, the member states of the newly formed United Nations gathered together to create the World Health Organization. A cholera epidemic that took 20,000 lives in Egypt in 1947 and 1948 helped spur the international community to action.
One of the greatest accomplishments of the international health community since then was the eradication of smallpox. The last naturally occurring case of the infection was recorded in 1977. But in a strange way, success with smallpox bred overconfidence and subsequent efforts to eradicate malaria and other diseases have not been as effective. Indeed, there is now debate within the global health community as to whether eradication campaigns should be abandoned in favor of less costly and perhaps more effective primary health and containment programs.
Global health is a research field at the intersection of medical and social science disciplines--including demography, economics, epidemiology, political economy and sociology. From different disciplinary perspectives, it focuses on determinants and distribution of health in international contexts.
An epidemiological perspective identifies major global health problems. A medical perspective describes the pathology of major diseases, and promotes prevention, diagnosis, and treatment of these diseases.
An economic perspective, emphasizes the cost-effectiveness and cost-benefit approaches for both individual and population health allocation. Aggregate analysis, eg from the perspective of governments and N.G.O.s, focuses on analysis for the health sector. Cost-effectiveness analysis compares the costs and health effects of an intervention to assess whether health investments are worthwhile from economic perspective. It is necessary to distinguish between independent interventions and mutually exclusive interventions. For independent interventions, average cost-effectiveness ratios suffice. However, when mutually exclusive interventions are compared, it is essential to use incremental cost-effectiveness ratios. The latter comparisons suggest how to achieve maximal health care effects from the available resources.
Individual health analysis from this perspective focuses on the demand and supply of health. The demand for health care is derived from the general demand for health. Health care is demanded as a means for consumers to achieve a larger stock of "health capital." The optimal level of investment in health occurs where the marginal cost of health capital is equal to the marginal benefit resulting from it (MC=MB). With the passing of time, health depreciates at some rate δ. The general interest rate in the economy is denoted by r. Supply of health focuses on provider incentives, market creation, market organization, issues related to information asymmetries, the role of NGOs and governments in health provision.
Another, ethical approach, emphasizes distributional considerations. The Rule of Rescue, coined by A.R. Jonsen (1986), is one way to address distributional issues. This rule specifies that it is 'a perceived duty to save endangered life where possible'. John Rawls ideas on impartial justice is a contractual perspective on distribution. These ideas have been applied by Amartya Sen  to address key aspects of health equity. Bioethics research also examines international obligations of justice, in three broadly clustered areas: (1) When are international inequalities in health unjust?; (2) Where do international health inequalities come from?; (3) How do we meet health needs justly if we can't meet them all?
A political approach, emphasizes political economy considerations applied to global health. Political economy originally was the term for studying production, buying and selling, and their relations with law, custom, and government. Originating in moral philosophy (e.g. Adam Smith was Professor of Moral Philosophy at the University of Glasgow), political economy of health is the study of how economies of states — polities, hence political economy - influence aggregate population health outcomes.
Analysis of global health hinges on how to measure health burden. Several measures exist: DALY, QALY and mortality measurements. The choice of measures can be controversial and includes practical and ethical considerations.
Life expectancy is a statistical measure of the average life span (average length of survival) of a specified population. It most often refers to the expected age to be reached before death for a given human population (by nation, by current age, or by other demographic variables). Life expectancy may also refer to the expected time remaining to live, and that too can be calculated for any age or for any group.
The disability-adjusted life year (DALY) is a summary measure that combines the impact of illness, disability and mortality on population health. The DALY combines in one measure the time lived with disability and the time lost due to premature mortality. One DALY can be thought of as one lost year of ‘healthy’ life and the burden of disease as a measurement of the gap between current health status and an ideal situation where everyone lives into old age free of disease and disability. For example, DALYs for a disease are the sum of the years of life lost due to premature mortality (YLL) in the population and the years lost due to disability (YLD) for incident cases of the health condition. One DALY represents the loss of one year of equivalent full health.
Quality-adjusted life years, or QALYs, is a way of measuring disease burden, including both the quality and the quantity of life lived, as a means of quantifying in benefit of a medical intervention. The QALY model requires utility independent, risk neutral, and constant proportional tradeoff behaviour. QALYs attempt to combine expected survival with expected quality of life into a single number: if an additional year of healthy life expectancy is worth a value of one (year), then a year of less healthy life expectancy is worth less than one (year). QALY calculations are based on measurements of the value that individuals place on expected years of survival. Measurements can be made in several ways: by techniques that simulate gambles about preferences for alternative states of health, with surveys or analyses that infer willingness to pay for alternative states of health, or through instruments that are based on trading off some or all likely survival time that a medical intervention might provide in order to gain less survival time of higher quality. QALYs are useful for utalitarian analysis, but does not in itself incorporate equity considerations.
Life expectancy and DALYs/QALYs represent the average disease burden well. However, infant mortality and under-five child mortality are more specific in representing the health in the poorest sections of a population. Therefore, changes in these classic measures are especially useful when focusing on health equity.  These measures are also important for advocates of children's rights. Approximately 56 million people died in 2001. Of these, 10.6 million were children under 5 years of age, 99% of these children were living in low-and middle-income countries. That translates to roughly 30,000 children dying every day.
Morbidity measure include incidence rate, prevalence and cumulative incidence. Incidence rate is the risk of developing some new condition within a specified period of time. Although sometimes loosely expressed simply as the number of new cases during some time period, it is better expressed as a proportion or a rate with a denominator.
Infections of the respiratory tract and middle ear are major causes of infant and child mortality. In adults, tuberculosis is highly prevalent and causes significant morbidity and mortality. Mortality in tuberculosis has increased due to the spread of HIV. The spread of respiratory infections is increased in crowded conditions. Current vaccination programmes against pertussis prevent 600 000 deaths each year. Measles is caused by the morbillivirus and spread via the airways. It is highly contagious and characterized by flulike symptoms including fever, cough, and rhinitis and after a few days deveopment of a generalized rash. It can effectively be prevented by vaccination. In spite of this, almost 200,000 people, mostly children under 5 years of age, died in measles in 2007. Pneumococci and Haemophilus influensae cause approximately 50 % of child deaths in pneumonia, and also cause bacterial menigitis and sepsis. Novel vaccines against pneumococci and Haemophilus influensa are clearly cost-effective in low-income countries. Universal use of these two vaccines are estimated to prevent at least 1 000 000 child deaths annually. For maximal long-term effect, vaccination of children should be integrated with primary health care measures 
Diarrhoeal infections are responsible for 17 per cent of deaths among children under the age of five worldwide, making them the second most common cause of child deaths globally. Poor sanitation can lead to increased transmission through water, food, utensils, hands and flies. Rotavirus is highly contagious and a major cause of severe diarrhoea and death (ca 20%) in children. According to the WHO, hygienic measures alone are insufficient for the prevention of rotavirus diarrhoea. Rotavirus vaccines are highly protective, safe and potentially cost-effective. Dehydration due to diarrhoea can be effectively treated through oral rehydration therapy (ORT), with dramatic reductions in mortality. By mixing water, sugar and salt and administering it to the affected child, dehydration can be treated. Important nutritional measures are promotion of breastfeeding and zinc supplementation.
Human immunodeficiency virus (HIV) is a retrovirus that first appeared in humans in the early 1980s. HIV progresses to a point where the infected person has AIDS or Acquired Immunodeficiency Syndrome. HIV becomes AIDS because the virus had depleted CD4+ T-cells that are necessary for a healthy immune system. Antiretroviral drugs prolong life and delay the onset of AIDS by minimizing the amount of HIV in the body.
HIV is transmitted through bodily fluids. Unprotected sex, intravenous drug use, blood transfusions, and unclean needles spread HIV through blood and other fluids. Once thought to be a disease that only affected drug users and homosexuals, it can affect anyone. Globally, the primary method of spreading HIV is through heterosexual intercourse. It can also be passed from a pregnant woman to her unborn child during pregnancy, or after pregnancy through breast milk. While it is a global disease that can affect anyone, there are disproportionately high infection rates in certain regions of the world.
Malaria is an infectious disease caused by protozoan Plasmodium parasites. The infection is transmitted via mosquito bites. Early symptoms may include fever, headaches, chills and nausea. Each year approximately 500 million cases of malaria occur worldwide, most commonly among children and pregnant women in underdeveloped countries. Malaria can hinder economic development of a country. Economic effects of malaria include decreased work productivity, treatment cost and time spent for getting treatment  Deaths in malaria can be sharply and cost-effectively reduced by use of insecticide-treated bednets, prompt artemisin-based combination therapy and supported by intermittent preventive treatment in pregnancy. However, only 23% of children and 27% of pregnant women in Africa were estimated to sleep under insecticide-treated bednets 
Greater than two billion people in the world are at risk of micronutrient deficiencies (including lack of vitamin A, iron, iodine and zinc). Among children under the age of five in the developing world, malnutrition contributes to 53% of deaths associated with infectious diseases. Malnutrition impairs the immune system, thereby increasing the frequency, severity, and duration of childhood illnesses (including measles, pneumonia and diarrhoea). Micronutrient deficiencies also compromise intellectual potential, growth, development and adult productivity.
However, infection is also an important cause and contributor to malnutrition. For example, gastrointestinal infections causes diarrhoea, and HIV, tuberculosis, intestinal parasites and chronic infection increase wasting and anemia.
Fifty million children under the age of five are affected by vitamin A deficiency. Such deficiency has been linked with night blindness. Severe vitamin A deficiency is associated with xerophtalmia and ulceration of the cornea, a condition that can lead to total blindness. Vitamin A is also involved in the function of the immune system and in maintaining epithelial surfaces. For this reason, vitamin A deficiency leads to increased susceptibility to infection and disease. In fact, vitamin A supplementation was shown to reduce child mortality rates by 23% link title in areas with significant levels of vitamin A deficiency.
Iron deficiency affects approximately one-third of the worlds' women and children. Iron deficiency contributes to anemia along with other nutritional deficiencies and infections and is associated with maternal mortality, prenatal mortality and mental retardation globally. In anemic children, iron supplementation combined with other micronutrients improves health and hemoglobin levels. In children, iron deficiency compromises learning capacity, and emotional and cognitive development.
Iodine deficiency is the leading cause of preventable mental retardation. As many as 50 million infants born annually are at risk of iodine deficiency. Pregnant women whom are iodine deficient should be included in the target population for this particular intervention because pregnant women with iodine defiency increases the chance of miscarriages and also lowers the development potential of the infant. Global efforts for universal salt iodization are helping eliminate this problem.
According to Lasserini and Fischer et al., zinc deficiency may increase the risk of mortality from diarrhea, pneumonia and malaria.  Almost 30% of the worlds children are thought to be zinc deficient. Supplements have been shown to reduce the duration of diarrhea episodes.
Interventions to prevent malnutrition include micronutrient supplementation, fortification of basic grocery foods, dietary diversification, hygienic measures to reduce spread of infections and promotion of breastfeeding. Dietary diversification aims to increase the consumption of vital micronutrients in the regular diet. This is done by education and promotion of a diverse diet, and by improving access to micronutrient rich and locally produced food.
The relative importance of chronic non-infectious disease is increasing. For example, the rates of type 2 diabetes, associated with obesity, have been on the rise in countries traditionally noted for hunger levels. In low-income countries, the number of individuals with diabetes is expected to increase from 84 million to 228 million by 2030. Obesity is preventable and is associated with numerous chronic diseases including cardiovascular conditions, diabetes, stroke, cancers and respiratory diseases. About 16% of the global burden of disease, measured as DALYs, has been accounted for by obesity.
Evidence based interventions for improved child health and survival include: Promotion of breastfeeding, zinc supplementation, vitamin A fortification and supplementation, salt iodization, handwashing and hygiene interventions, vaccination, treatment of severe acute malnutrition. In malaria endemic regions insecticide treated bednets and intermittent pharmacological treatment reduce mortality.   . Based on such studies the Global Health Council suggests a list of 32 treatment and intervention measures that could potentially save several million lives each year.
To be most effective, interventions need to be appropriate in the local context, be timely and equitable and achieve maximum coverage of the target population. Interventions with only partial coverage may not be cost-effective. For example, immunization programs with partial coverage often fail to reach the ones at greatest risk of disease. Furthermore, coverage estimates may be misleading if not distribution is taken into account. Thus, mean national coverage may appear fairly adequate, but may nevertheless be insufficient when analyzed in detail. This has been termed 'the fallacy of coverage'. 
Progress in coverage of health interventions, especially relating to child and maternal health (Millennium Development Goals 4 and 5), is tracked in 68 low-income countries by a UNICEF led collaboration called Countdown to 2015. These countries are estimated to account for 97% of maternal and child deaths.
Jacobsen KH (2008) Introduction to Global Health. Jones and Bartlett
Skolnik R (2008) Essential Public Health: Essentials of Global Health. Jones and Bartlett.
Levine R (Ed) (2007) Essential Public Health: Case Studies in Global Health. Jones and Bartlett.
These books have been adopted by the Faculty of Health & Social Care at the University of Hull. They are essential reading for the BSc Global Health and Disease (International Health Development and Humanitarian Relief) and the Current Issues in World Health Module I and the Current Issues in World Health II modules.