Adolescence is the phase of life between childhood and adulthood, from ages 10 to 19. It is a unique stage of human development and an important time for laying the foundations of good health. Adolescents experience rapid physical, cognitive and psychosocial growth. This affects how they feel, think, make decisions, and interact with the world around them.

Today, the Africa Regional Certification Commission certified the WHO African Region as wild polio-free after four years without a case. With this historic milestone, five of the six WHO regions – representing over 90% of the world’s population – are now free of the wild poliovirus, moving the world closer to achieving global polio eradication.

Every person – in every country in the world – should have the opportunity to live a long and healthy life. Yet, the environments in which we live can favour health or be harmful to it. Environments are highly influential on our behaviour and our exposure to health risks (for example air pollution, violence), our access to services (for example, health and social care) and the opportunities that ageing brings.

Antimicrobial resistance (AMR) threatens the effective prevention and treatment of an ever-increasing range of infections caused by bacteria, parasites, viruses and fungi. AMR occurs when bacteria, viruses, fungi and parasites change over time and no longer respond to medicines making infections harder to treat and increasing the risk of disease spread, severe illness and death. As a result, the medicines become ineffective and infections persist in the body, increasing the risk of spread to others. Antimicrobials - including antibiotics, antivirals, antifungals and antiparasitics - are medicines used to prevent and treat infections in humans, animals and plants. Microorganisms that develop antimicrobial resistance are sometimes referred to as “superbugs”.

Nearly 120 million units of blood are donated every year. However, this is not sufficient to meet the global need many patients requiring a transfusion do not have timely access to safe blood. Blood cannot be stored indefinitely, meaning there is a constant need for donations. Regular donations are required to ensure there is always a supply for those in need. Despite global need, donation rates differ around the world and some high-income countries see up to seven times more donations than low-income countries.

Breastfeeding is one of the most effective ways to ensure child health and survival. However, nearly 2 out of 3 infants are not exclusively breastfed for the recommended 6 months—a rate that has not improved in 2 decades. Breastmilk is the ideal food for infants. It is safe, clean and contains antibodies which help protect against many common childhood illnesses. Breastmilk provides all the energy and nutrients that the infant needs for the first months of life, and it continues to provide up to half or more of a child’s nutritional needs during the second half of the first year, and up to one third during the second year of life.

Cancer is the uncontrolled growth and spread of cells. It can affect almost any part of the body. The growths often invade surrounding tissue and can metastasize to distant sites. Many cancers can be prevented by avoiding exposure to common risk factors, such as tobacco smoke. In addition, a significant proportion of cancers can be cured, by surgery, radiotherapy or chemotherapy, especially if they are detected early.

Cardiovascular diseases (CVDs) are the number 1 cause of death globally, taking an estimated 17.9 million lives each year. CVDs are a group of disorders of the heart and blood vessels and include coronary heart disease, cerebrovascular disease, rheumatic heart disease and other conditions. Four out of 5 CVD deaths are due to heart attacks and strokes, and one third of these deaths occur prematurely in people under 70 years of age.

Chagas disease, also known as American trypanosomiasis, is a potentially life-threatening illness caused by the protozoan parasite Trypanosoma cruzi.

Protecting and improving the health of children is of fundamental importance. Over the past several decades, we have seen dramatic progress in improving the health and reducing the mortality rate of young children. Among other encouraging statistics, the number of children dying before the age of 5 was halved from 2000 to 2017, and more mothers and children are surviving today than ever before. However, a great deal of work remains to further improve the health outcomes for children. The world is facing a double mandate. More than half of child deaths are due to conditions that could be easily prevented or treated given access to health care and improvements to their quality of life. At the same time, children must also be given a stable environment in which to thrive, including good health and nutrition, protection from threats and access to opportunities to learn and grow. Investing in children is one of the most important things a society can do to build a better future.

Cholera is an acute diarrhoeal infection caused by ingestion of food or water contaminated with the bacterium Vibrio cholerae. Cholera remains a global threat to public health and an indicator of inequity and lack of social development. Researchers have estimated that every year, there are 1.3 to 4.0 million cases, and 21 000 to 143 000 deaths worldwide due to cholera. Cholera is an extremely virulent disease that can cause severe acute watery diarrhoea with severe dehydration. It takes between 12 hours and 5 days for a person to show symptoms after ingesting contaminated food or water. Cholera affects both children and adults and can kill within hours if untreated. Most people infected with Vibrio cholerae do not develop any symptoms, although the bacteria are present in their faeces for 1-10 days after infection and are shed back into the environment, potentially infecting other people. Cholera is often predictable, preventable and can ultimately be eliminated where access to clean water and sanitation facilities, and satisfactory hygiene conditions are ensured and sustained for the whole population.

Climate change is impacting human lives and health in a variety of ways. It threatens the essential ingredients of good health - clean air, safe drinking water, nutritious food supply, and safe shelter - and has the potential to undermine decades of progress in global health. Between 2030 and 2050, climate change is expected to cause approximately 250 000 additional deaths per year, from malnutrition, malaria, diarrhoea and heat stress alone. The direct damage costs to health is estimated to be between USD 2-4 billion per year by 2030.

A person is said to have hearing loss if they are not able to hear as well as someone with normal hearing, meaning hearing thresholds of 20 dB or better in both ears. It can be mild, moderate, moderately severe, severe or profound, and can affect one or both ears. Major causes of hearing loss include congenital or early onset childhood hearing loss, chronic middle ear infections, noise-induced hearing loss, age-related hearing loss, and ototoxic drugs that damage the inner ear. The impacts of hearing loss are broad and can be profound. They include a loss of the ability to communicate with others delayed language development in children, which can lead to social isolation, loneliness and frustration, particularly among older people with hearing loss. Many areas lack sufficient accommodations for hearing loss, which effect academic performance and options for employment. Children with hearing loss and deafness in developing countries rarely receive any schooling. WHO estimates that unaddressed hearing loss costs the global economy US$ 750 billion annually due to health sector costs (excluding the cost of hearing devices), costs of educational support, loss of productivity and societal costs.

Dengue is a mosquito-borne viral disease that has rapidly spread in all regions of WHO in recent years. Dengue virus is transmitted by female mosquitoes mainly of the species Aedes aegypti and, to a lesser extent, Ae. albopictus. These mosquitoes are also vectors of chikungunya, yellow fever and Zika viruses. Dengue is widespread throughout the tropics, with local variations in risk influenced by rainfall, temperature, relative humidity and unplanned rapid urbanization.

Diabetes is a chronic, metabolic disease characterized by elevated levels of blood glucose (or blood sugar), which leads over time to serious damage to the heart, blood vessels, eyes, kidneys, and nerves. The most common is type 2 diabetes, usually in adults, which occurs when the body becomes resistant to insulin or doesn't make enough insulin. In the past three decades the prevalence of type 2 diabetes has risen dramatically in countries of all income levels. Type 1 diabetes, once known as juvenile diabetes or insulin-dependent diabetes, is a chronic condition in which the pancreas produces little or no insulin by itself. For people living with diabetes, access to affordable treatment, including insulin, is critical to their survival. There is a globally agreed target to halt the rise in diabetes and obesity by 2025.

Diagnostic imaging is the use of X-ray, ultrasound, radioactive isotopes, or magnetic resonance to produce a visual display or representation of structural and / or functional information of the "inside" of the human body. Diagnostic imaging, especially X-ray based examinations and ultrasonography, is crucial in every medical setting and at all levels of heath care. Though clinical judgment maybe sufficient in treating many conditions, the use of diagnostic imaging services is paramount in confirming, correctly assessing and documenting disease processes and also in judging the disease response to treatment.

Rehabilitation of people with disabilities is a process aimed at enabling them to reach and maintain their optimal physical, sensory, intellectual, psychological and social functional levels. Rehabilitation provides disabled people with the tools they need to attain independence and self-determination.

A serious disruption of the functioning of a community or a society causing widespread human, material, economic or environmental losses which exceed the ability of the affected community or society to cope using its own resources.

Dracunculiasis is rarely fatal, but infected people become non-functional for weeks and months. It affects people in rural, deprived, and isolated communities who depend mainly on open stagnant surface water sources such as ponds for drinking water.

Countries in the greater Horn of Africa are facing food insecurity not seen in decades with millions of people at risk of starvation. The region is reeling from the worst drought in 40 years and other climate shocks, years of conflict and instability, the impact of the pandemic and rising global food prices. A hunger crisis is a health crisis. Displacement often leads to an increase in infectious diseases, and malnutrition makes people more likely to get sick. Many families have left their homes in search of food, water and pasture for animals. Uprooted, they often lack access to health services just when they are needed most. This is why health response images are included in this photo gallery.

Ebola virus disease (EVD), formerly known as Ebola haemorrhagic fever, is a severe, often fatal illness affecting humans and other primates. The virus is transmitted to people from wild animals (such as fruit bats, porcupines and non-human primates) and then spreads in the human population through direct contact with the blood, secretions, organs or other bodily fluids of infected people, and with surfaces and materials (e.g. bedding, clothing) contaminated with these fluids. The average EVD case fatality rate is around 50%. Case fatality rates have varied from 25% to 90% in past outbreaks. The first EVD outbreaks occurred in remote villages in Central Africa, near tropical rainforests. The 2014–2016 outbreak in West Africa was the largest and most complex Ebola outbreak since the virus was first discovered in 1976. There were more cases and deaths in this outbreak than all others combined. It also spread between countries, starting in Guinea then moving across land borders to Sierra Leone and Liberia. It is thought that fruit bats of the Pteropodidae family are natural Ebola virus hosts.

Course of study required to educate a legally qualified and licensed practitioner of medicine, concerned with maintaining or restoring human health through the study, diagnosis and treatment of disease and injury, through the science of medicine and the applied practice of that science. Gaining a basic medical degree may take from five to eight or even nine years, depending on jurisdiction and university. Medical doctors include generalists and specialists. Medical training completed by internship qualifies a medical doctor to become a physician or a surgeon.

An integrated global alert and response system for epidemics and other public health emergencies based on strong national public health systems and capacity and an effective international system for coordinated response.

Access to appropriate medications is shown to have substantial impacts on community health and the related economic indicators. Quality-assured, safe and effective medicines, vaccines and medical devices are fundamental to a functioning health system. However, globalized trade can undermine regulation, and in resource-limited settings especially, incidence of substandard or falsified medicines is growing. Working to increase access to essential pharmaceuticals while limiting the spread of falsified products is at the heart of WHO’s global strategy on medicines.

Access to sufficient amounts of safe and nutritious food is key to sustaining life and promoting good health. Unsafe food containing harmful bacteria, viruses, parasites or chemical substances can cause more than 200 different diseases – ranging from diarrhoea to cancers. Around the world, an estimated 600 million – almost 1 in 10 people – fall ill after eating contaminated food each year, resulting in 420 000 deaths and the loss of 33 million healthy life years (DALYs).

Gender refers to the characteristics of women, men, girls and boys that are socially constructed. This includes norms, behaviours and roles associated with being a woman, man, girl or boy, as well as relationships with each other. As a social construct, gender varies from society to society and can change over time. Gender is hierarchical and produces inequalities that intersect with other social and economic inequalities. Gender-based discrimination intersects with other factors of discrimination, such as ethnicity, socioeconomic status, disability, age, geographic location, gender identity and sexual orientation, among others. This is referred to as intersectionality.

Environmental health addresses all the physical, chemical, and biological factors external to a person, and all the related factors impacting behaviours. It encompasses the assessment and control of those environmental factors that can potentially affect health. It is targeted towards preventing disease and creating health-supportive environments. This definition excludes behaviour not related to environment, as well as behaviour related to the social and cultural environment, and genetics.

Statistics refers to both quantitative data, and the classification of such data in accordance with probability theory and the application to them of methods such as hypothesis testing. Health statistics include both empirical data and estimates related to health, such as mortality, morbidity, risk factors, health service coverage, and health systems. The production and dissemination of health statistics is a core WHO activity mandated to WHO by its Member States in its Constitution. WHO programmes compile and disseminate a broad range of statistics that play a key role in advocacy for health issues, monitoring and evaluation of health programmes and provision of technical assistance to countries.

The first International Conference on Health Promotion was held in Ottawa in 1986, and was primarily a response to growing expectations for a new public health movement around the world. It launched a series of actions among international organizations, national governments and local communities to achieve the goal of "Health For All" by the year 2000 and beyond. The basic strategies for health promotion identified in the Ottawa Charter were: advocate (to boost the factors which encourage health), enable (allowing all people to achieve health equity) and mediate (through collaboration across all sectors). Since then, the WHO Global Health Promotion Conferences have established and developed the global principles and action areas for health promotion. Most recently, the 9th global conference (Shanghai 2016), titled ‘Promoting health in the Sustainable Development Goals: Health for all and all for health’, highlighted the critical links between promoting health and the 2030 Agenda for Sustainable Development. Whilst calling for bold political interventions to accelerate country action on the SDGs, the Shanghai Declaration provides a framework through which governments can utilize the transformational potential of health promotion.

Laboratory networks are essential to support disease surveillance and outbreak investigation. Formalized networks facilitate the exchange of knowledge and expertise, thus facilitating timely and appropriate support to surveillance and epidemiology. Laboratory biosafety procedures and practices describe ways to appropriately handle and work with pathogens, minimizing the risk of exposure and infection.

Health systems can only function with health workers; improving health service coverage and realizing the right to the enjoyment of the highest attainable standard of health is dependent on their availability, accessibility, acceptability and quality. WHO estimates a projected shortfall of 18 million health workers by 2030, mostly in low- and lower-middle income countries. However, countries at all levels of socioeconomic development face, to varying degrees, difficulties in the education, employment, deployment, retention, and performance of their workforce.

Human immunodeficiency virus (HIV) is an infection that attacks the body’s immune system, specifically the white blood cells called CD4 cells. HIV destroys these CD4 cells, weakening a person’s immunity against infections such as tuberculosis and some cancers.

Hospitals play an important role in the health care system. They are health care institutions that have an organized medical and other professional staff, and inpatient facilities, and deliver medical, nursing and related services 24 hours per day, 7 days per week. Hospitals offer a varying range of acute, convalescent and terminal care using diagnostic and curative services in response to acute and chronic conditions arising from diseases as well as injuries and genetic anomalies. In doing so they generate essential information for research, education and management. Traditionally oriented on individual care, hospitals are increasingly forging closer links with other parts of the health sector and communities in an effort to optimize the use of resources for the promotion and protection of individual and collective health status.

Immunization is a global health and development success story, saving millions of lives every year. Vaccines reduce risks of getting a disease by working with your body’s natural defences to build protection. When you get a vaccine, your immune system responds. We now have vaccines to prevent more than 20 life-threatening diseases, helping people of all ages live longer, healthier lives. Immunization currently prevents 2-3 million deaths every year from diseases like diphtheria, tetanus, pertussis, influenza and measles. Immunization is a key component of primary health care and an indisputable human right. It’s also one of the best health investments money can buy. Vaccines are also critical to the prevention and control of infectious-disease outbreaks. They underpin global health security and will be a vital tool in the battle against antimicrobial resistance.

Equity is the absence of avoidable or remediable differences among groups of people, whether those groups are defined socially, economically, demographically or geographically. Health inequities involve more than inequality with respect to health determinants, access to the resources needed to be healthy or health outcomes. They also entail a failure to avoid or overcome inequalities that infringe on fairness. Reducing health inequities is important because health is a fundamental human right. However, evidence suggests that the impressive health gains achieved over recent decades are unequally distributed and have largely failed to reach the poor and other marginalized or socially excluded groups. Persistent and growing inequalities in health are increasingly evident, both between and within countries.

Seasonal influenza is an acute respiratory infection caused by influenza viruses which circulate in all parts of the world. It represents a year-round disease burden. It causes illnesses that range in severity and sometimes lead to hospitalization and death. Most people recover from fever and other symptoms within a week without requiring medical attention. However, influenza can cause severe illness or death, particularly among high risk groups including the very young, the elderly, pregnant women, health workers and those with serious medical conditions. In temperate climates, seasonal epidemics occur mainly during winter, while in tropical regions, influenza may occur throughout the year, causing outbreaks more irregularly.

The leishmaniases are a group of diseases caused by protozoan parasites from more than 20 Leishmania species. These parasites are transmitted to humans by the bite of an infected female phlebotomine sandfly, a tiny – 2–3 mm long – insect vector.

Leprosy, also known as Hansen’s disease, is a chronic infectious disease caused by Mycobacterium leprae. The disease mainly affects the skin, the peripheral nerves, mucosal surfaces of the upper respiratory tract and the eyes. Leprosy is known to occur at all ages ranging from early infancy to very old age. Leprosy is curable and early treatment averts most disabilities.

Leptospirosis is a zoonotic disease with epidemic potential, especially after a heavy rainfall, caused by a bacterium called Leptospira. Leptospira interrogans is pathogenic to humans and animals, with more than 200 serologic variants or serovars. Humans usually acquire leptospirosis through direct contact with the urine of infected animals or a urine-contaminated environment. Human-to-human transmission occurs only very rarely.

Lymphatic filariasis, commonly known as elephantiasis, is a neglected tropical disease. Infection occurs when filarial parasites are transmitted to humans through mosquitoes. Infection is usually acquired in childhood causing hidden damage to the lymphatic system.

Malaria is caused by parasites that are transmitted to people through the bites of infected female mosquitoes. P. falciparum is the most deadly malaria parasite and the most prevalent in Africa, where malaria cases and deaths are heavily concentrated. The first symptoms of malaria – fever, headache, chills and vomiting – usually appear between 10 and 15 days after the mosquito bite. Without prompt treatment, P. falciparum malaria can progress to severe illness and death. WHO recommends a multi-pronged strategy to prevent, control and eliminate malaria. Key interventions include: the use of insecticide-treated mosquito nets and indoor residual spraying, diagnostic testing, and treatment of confirmed cases with effective anti-malarial medicines. In recent years, these measures have dramatically lowered the malaria burden in many settings. Malaria transmission continues in many countries around the world however, and causes hundreds of thousands of deaths each year.

Maternal health refers to the health of women during pregnancy, childbirth and the postnatal period. Each stage should be a positive experience, ensuring women and their babies reach their full potential for health and well-being.

Measles is a highly contagious viral disease whose common complications include pneumonia and diarrhoea. Death may occur in up to 5-10% of infected young children in developing countries. Rubella is also a contagious viral disease, but milder than measles. However, when rubella infects a pregnant woman during the first half of her pregnancy, there is danger of fetal death or birth defects affecting primarily the eyes, ears, heart, and brain.

Mental health refers to a broad array of activities directly or indirectly related to the mental well-being component included in the WHO's definition of health: "A state of complete physical, mental and social well-being, and not merely the absence of disease". It is related to the promotion of well-being, the prevention of mental disorders, and the treatment and rehabilitation of people affected by mental disorders. The harmful use of alcohol is a global problem which compromises both individual and social development. It results in 3.3 million deaths each year. Alcohol is the world's third largest risk factor for premature mortality, disability and loss of health; it is the leading risk factor in the Western Pacific and the Americas and the second largest in Europe. Alcohol is associated with many serious social and developmental issues, including violence, child neglect and abuse, and absenteeism in the workplace. It also causes harm far beyond the physical and psychological health of the drinker. It harms the well-being and health of people around the drinker. An intoxicated person can harm others or put them at risk of traffic accidents or violent behaviour, or negatively affect co-workers, relatives, friends or strangers. Thus, the impact of the harmful use of alcohol reaches deep into society.