PUBLIC HEALTH
Immunization
Immunization, is the process by which an individual's immune system becomes fortified against an agent (known as the immunogen).
Immunization is the process whereby a person is made immune or resistant to an infectious disease, typically by the administration of a vaccine. Vaccines stimulate the body’s own immune system to protect the person against subsequent infection or disease.
Immunization is a proven tool for controlling and eliminating life-threatening infectious diseases and is estimated to avert over 2 million deaths each year. It is one of the most cost-effective health investments, with proven strategies that make it accessible to even the most hard-to-reach and vulnerable populations. It has clearly defined target groups; it can be delivered effectively through outreach activities; and vaccination does not require any major lifestyle change.
When an immune system is exposed to molecules that are foreign to the body (non-self), it will orchestrate an immune response, but it can also develop the ability to quickly respond to a subsequent encounter (through immunological memory). This is a function of the adaptive immune system. Therefore, by exposing an animal to an immunogen in a controlled way, their body can learn to protect itself: this is called active immunization.
The most important elements of the immune system that are improved by immunization are the B cells (and the antibodies they produce) and T cells. Memory B cell and memory T cells are responsible for a swift response to a second encounter with a foreign molecule. Passive immunization is when these elements are introduced directly into the body, instead of when the body itself has to make these elements.
Immunization can be done through various techniques, most commonly vaccination. Vaccines against microorganisms that cause diseases can prepare the body's immune system, thus helping to fight or prevent an infection. The fact that mutations can cause cancer cells to produce proteins or other molecules that are unknown to the body forms the theoretical basis for therapeutic cancer vaccines. Other molecules can be used for immunization as well, for example in experimental vaccines against nicotine (NicVAX) or the hormone ghrelin (in experiments to create an obesity vaccine).
Passive and active immunization
Immunization can be achieved in an active or passive fashion: vaccination is an active form of immunization.
Active immunization
Active immunization entails the introduction of a foreign molecule into the body, which causes the body itself to generate immunity against the target. This immunity comes from the T cells and the B cells with their antibodies.
Active immunization can occur naturally when a person comes in contact with, for example, a microbe. If the person has not yet come into contact with the microbe and has no pre-made antibodies for defense (like in passive immunization), the person becomes immunized. The immune system will eventually create antibodies and other defenses against the microbe. The next time, the immune response against this microbe can be very efficient; this is the case in many of the childhood infections that a person only contracts once, but then is immune.
Artificial active immunization is where the microbe, or parts of it, are injected into the person before they are able to take it in naturally. If whole microbes are used, they are pre-treated. Depending on the type of disease, this technique also works with dead microbes, parts of the microbe, or treated toxins from the microbe.
Passive immunization
Main article: Passive immunity
Passive immunization is where pre-made elements of the immune system are transferred to a person, and the body doesn't have to create these elements itself. Currently, antibodies can be used for passive immunization. This method of immunization begins to work very quickly, but it is short lasting, because the antibodies are naturally broken down, and if there are no B cells to produce more antibodies, they will disappear.
Passive immunization can be naturally acquired when antibodies are being transferred from mother to fetus during pregnancy, to help protect the fetus before and shortly after birth.
Artificial passive immunization is normally given by injection and is used if there has been a recent outbreak of a particular disease or as an emergency treatment to poisons (for example, for tetanus). The antibodies can be produced in animals or in vitro.

Immunization, Vaccines and Biologicals.
IVB topics
Here is a list of topics and concerns that IVB deal with. Click on a heading to receive further information on that topic.
Diseases and Vaccines
Tuberculosis
An estimated one third of humanity (approximately two billion people) is infected with tuberculosis (TB). Amongst those carrying the pathogen, around 8 million persons come down with clinical disease every year; and out of these, about 1.6 million die, not counting tuberculosis-related deaths in TB-HIV co-infected individuals. Over 1.5 million new TB cases per year occur in sub-Saharan Africa, nearly three million in South-East Asia and over a quarter of a million in Eastern Europe. In 1993, WHO declared tuberculosis a global emergency, reflecting the magnitude of the concern about the TB epidemic. It is estimated that between 2000 and 2020, nearly one billion people will be newly infected, 200 million will get sick, and 35 million will die from TB – if control measures are not significantly improved.
Cholera
Cholera is an acutely dehydrating, watery diarrhoeal disease caused by intestinal infection with Vibrio cholerae. It probably has existed on the Indian subcontinent for thousands of years as can be judged from ancient manuscripts. Cholera was repeatedly one of the most dreaded pandemic diseases in history, being able to spread rapidly to large numbers of people, of whom a high proportion died. Before the advent of an effective rehydration therapy, cholera epidemics were associated with case–fatality rates exceeding 40% and led to tens of thousands of deaths. Cholera remains today an important disease in areas where population overcrowding and poor sanitation are common, such as in slums and refugee camps in developing countries. The year 1991 was marked by the entry of V. cholerae into Peru and other Andean countries, from which it has since spread throughout South and Central America. This was the first time cholera had invaded the Americas in more than 100 years. More
Dengue
Dengue fever, a usually mild albeit debilitating viral fever (breakbone fever), is prevalent throughout the tropics, where the urban-dwelling mosquito Aedes aegypti is a major vector. The dengue viruses are the most widespread arthropod-borne viruses (arboviruses).. During the 20th century, the distribution and density of Aedes aegypti expanded dramatically in tropical areas, beginning in large cities then spreading to the countryside. This was followed by global circulation of the four virus types.
Because there is no cross protection between different dengue viruses, an individual can be sequentially infected by different virus types. Most primary infections cause a debilitating, but nonfatal, form of illness. Some patients, particularly children but increasingly adults, experience more severe and occasionally fatal forms of the disease, including dengue haemorrhagic fever. The presence of antibodies to one type of dengue virus is believed to facilitate the occurrence of dengue haemorrhagic fever in certain individuals through immune-enhancement when infected by a second serotype. It is estimated that from 50–100 million cases of dengue fever, 500 000 cases of severe forms and more than 20 000 deaths occur each year.
While vector control can show impact if systematically applied, most hopes rely on vaccines for the prevention of the disease. Vaccine development has been ongoing for decades, and has been hampered by the need to protect against all four viruses, as well as by concerns of immune-enhancement. Much progress has been reported over the past years, and several vaccine candidates are now in clinical development.
Diphtheria
Diphtheria is caused by the bacterium Corynebacterium diphtheriae. This germ produces a toxin that can harm or destroy human body tissues and organs. One type of diphtheria affects the throat and sometimes the tonsils. Another type, more common in the tropics, causes ulcers on the skin.
Diphtheria affects people of all ages, but most often it strikes unimmunized children. In temperate climates, diphtheria tends to occur during the colder months. In 2000, 30 000 cases and 3000 deaths of diphtheria were reported worldwide.
Enterotoxigenic Escherichia coli
Disease caused by ETEC follows ingestion of contaminated food or water and is characterized by profuse watery diarrhoea lasting for several days. It may lead to dehydration and malnutrition in young children in developing countries. ETEC is the most frequently isolated enteropathogen in community-based studies of children aged less than 5 years in the developing world, and probably accounts for approximately 200 million diarrhoea episodes and 380 000 deaths annually. The peak incidence of ETEC diarrhoea in these settings occurs in the first two years of life, with a declining incidence with age thereafter. Surveillance of hospitalized cases of ETEC diarrhoea has however shown that almost half the cases occur in individuals over 10 years of age. In children, the tendency of ETEC to cause dehydrating diarrhoea is lower (approximately 5% of episodes) than that of rotavirus (approximately 36% of episodes).
Epstein Barr virus
The primary site of Epstein-Barr virus (EBV) infection is the oropharyngeal cavity. Children and teenagers are commonly afflicted usually after oral contact, hence the name “kissing disease”. Based on serology, about 95% of the world adult population has been infected with EBV and, following primary infection, remains lifelong carriers of the virus. In developed countries, exposure to EBV occurs relatively late: only 50–70% of adolescents and young adults are EBV seropositive. About 30% of the seronegative group will develop infectious mononucleosis as a result of primary EBV infection. The disease is characterized by fever, sore throat, generalized lymphadenopathy, splenomegaly, intense asthenia, hyper-lymphocytosis (>50%) with atypical lymphocytes and elevated transaminase levels. In developing countries, EBV antibodies are acquired early in life and the disease is mostly asymptomatic.
Hepatitis B
Hepatitis B virus causes a life-threatening liver infection that often leads to chronic liver disease and puts people at high risk of death from cirrhosis of the liver and liver cancer. Hepatitis B virus infection is a major global health problem. Worldwide, an estimated two billion people have been infected with the hepatitis B virus (HBV), and more than 350 million have chronic (long-term) liver infections.
A vaccine against hepatitis B has been available since 1982. Hepatitis B vaccine is 95% effective in preventing HBV infection and its chronic consequences, and is the first vaccine against a major human cancer. The vaccine has an outstanding record of safety and effectiveness. Since 1982, over one billion doses of hepatitis B vaccine have been used worldwide. In many countries where 8% to 15% of children used to become chronically infected with HBV, vaccination has reduced the rate of chronic infection to less than 1% among immunized children.
As at December 2007, 171 countries reported that they had included the hepatitis B vaccine into their national infant immunization programmes (two of these countries reported introducing in part of the country only). This is a major increase compared with 31 countries in 1992, the year that the World Health Assembly passed a resolution to recommend global vaccination against hepatitis B.
Hepatitis C
Herpes virus type 2
Herpes simplex virus type 2 (HSV-2) is the cause of genital herpes. The hallmark of herpesvirus infections is the establishment of a lifelong, latent infection that can reactivate to cause one or more rounds of disease. Latent HSV-2 infection occurs primarily in neurons found in the sacral root ganglia. The clinical spectrum of HSV-2 includes primary infection, characterized by the appearance of vesicles on the vulva or the penis that soon break to leave shallow, painful ulcerating lesions. The ulcers heal in 2–3 weeks, although healing may be very slow in immunocompromised patients. Primary infection is then followed by recurrent episodes of clinical disease (4–5 per year). The proportion of symptomatic infections is estimated to be between 13% and 37%, and probably higher in HIV positive individuals. Subclinical infection may be associated with infectious viral shedding. The virus is transmitted in genital secretions. Transmission of HSV-2 to newborns at the time of delivery may lead to devastating systemic infection with encephalitis. The risk of neonatal herpes fortunately is low among HIV-negative pregnant women living in industrialized countries (less than 3%), but few data are available on neonatal herpes in developing countries.
Haemophilus influenzae type b (Hib)
Haemophilus influenzae type b (Hib) is a bacteria responsible for severe pneumonia, meningitis and other invasive diseases almost exclusively in children aged less than 5 years. It is transmitted through the respiratory tract from infected to susceptible individuals.
In 2000, Hib was estimated to have caused two to three million cases of serious disease, notably pneumonia and meningitis, and 386 000 deaths in young children. Hib disease is observed in all parts of the world but is difficult to confirm because it requires prompt laboratory investigation in patients that have not received prior antibiotic treatment.
The vaccine is now used in the routine immunization schedule of more than 100 countries and WHO recommends the use of Hib conjugate vaccines in all countries. The vaccine is available in monovalent presentation or combined with DTP and other vaccine combinations including with hepatitis B and inactivated polio vaccines.
HIV / AIDS
Introduction
According to the 2007 WHO/UNAIDS estimates, at the end of 2007, 33.2 million people were living with HIV. Some 2,5 million people became newly infected that year and 2.1 million died of AIDS, which maintains AIDS as a leading cause of death in Africa.
More than 95% of HIV infections are in developing countries, two-thirds of them in sub-Saharan Africa, where over 28 million people are living with HIV. While infection rates are lower in Asia and the Pacific, where over 7 million are infected, there is a risk that localized epidemics involving mainly high-risk groups could spark off major epidemics in some of the world’s most populous countries. The disease is having a major impact on social and economic development. Poverty is increasing in many countries as households lose one or more breadwinners to AIDS. And both public services and private companies are reeling from the impact of HIV-related sickness and deaths among their workforce.
Human papillomavirus (HPV)
Human papillomaviruses are common throughout the world. Although most infections with HPV cause no symptoms, persistent genital HPV infection can cause cervical cancer in women. HPV can also cause other types of anogenital cancer, head and neck cancers, and genital warts, in both men and women. HPV are transmitted through sexual contact. HPV are estimated to cause about half a million cases of cervical cancer every year, and are the leading cause of death from cancer for women in the developing world.
For many years, the main way to prevent cervical cancer has been through screening programmes. Unfortunately, these have not been successfully implemented in most low-resource settings.
There are two HPV vaccines now being marketed in many countries throughout the world. Both vaccines are highly efficacious in preventing infection with virus types 16 and 18, which are together responsible for approximately 70% of cervical cancer cases globally. They are also highly efficacious in preventing precancerous cervical lesions caused by these types. One vaccine is also highly efficacious in preventing anogenital warts, a common genital disease which is virtually always caused by infection with HPV types 6 and 11. The primary target group in most of the countries recommending HPV vaccination is young adolescent girls. Data from clinical trials and initial post-marketing surveillance conducted in several continents show both vaccines to be safe.
As of mid-2008, HPV vaccines had been recommended for use in females through the national immunization programmes of more than 15 high-income countries and at least two middle-income countries.
Influenza
The burden of influenza in the USA is currently estimated to be 25–50 million cases per year, leading to 150 000 hospitalizations and 30 000–40 000 deaths. If these figures are extrapolated to the rest of the world, the average global burden of inter-pandemic influenza may be on the order of ~1 billion cases of flu, ~3–5 million cases of severe illness and 300 000–500 000 deaths annually. Epidemics and outbreaks of influenza occur in different seasonal patterns depending on the region in the world. In temperate climate zones, seasonal epidemics typically begin in the late fall and peak in mid- to late winter. In tropical zones, seasonal patterns appear to be less pronounced, with year-round isolation of virus.
In developed countries, annual influenza epidemics infect about 10–20% of the population each season, and cause febrile illnesses that range in severity from mild to debilitating and can lead in some instances to hospitalization and even cause death. The latter mostly occur as a consequence of primitive fulminant influenza virus pneumonia or of secondary respiratory bacterial infections and are facilitated by underlying pulmonary or cardiopulmonary pathologies. The risk of developing serious complications is aggravated in the very young and in the elderly. Data collected in Michigan (USA) and in Japan indicate that the mass vaccination of school-aged children correlates with a reduced rate of respiratory illness in all age groups, suggesting that larger-scale immunization in childhood could favorably affect influenza epidemics.
Malaria
Malaria is by far the world's most important tropical parasitic disease, killing more people than any other communicable disease except TB. Worldwide prevalence of the disease is in the order of 350–500 million clinical cases each year, with an estimated annual death toll of over 1.1 million deaths. The vast majority of deaths occur among children under five years of age, especially in remote rural areas with poor access to health services. One century ago, malaria was endemic across every continent except Antarctica. Control programmes based on the use of insecticides led to its elimination from Australia, Europe and the USA by the 1950s, but the disease still remains endemic in some 100 countries in Africa, the Americas, the Eastern Mediterranean Region, the South-East Asia Region, and the Western Pacific Region. These countries are inhabited by more than 2.4 billion people – 40% of the world's population
Measles
Measles is a highly contagious, serious disease caused by a virus. It remains a leading cause of death among young children globally, despite the availability of a safe and effective vaccine.
Measles is transmitted via droplets from the nose, mouth or throat of infected persons. Initial symptoms, which usually appear 10–12 days after infection, include high fever, runny nose, bloodshot eyes, and tiny white spots on the inside of the mouth. Several days later, a rash develops, starting on the face and upper neck and gradually spreading downwards.
Severe measles is more likely among poorly nourished young children, especially those with insufficient vitamin A, or whose immune systems have been weakened by HIV/AIDS or other diseases. Complications associated with measles cause most deaths. Complications are more common in children under the age of five or adults over the age of 20. The most serious complications include blindness, encephalitis (an infection that causes brain swelling), severe diarrhoea and related dehydration, ear infections, or severe respiratory infections such as pneumonia.
Mumps
Mumps is an infection caused by a virus. It is sometimes called infectious parotitis, and it primarily affects the salivary glands.
Mumps is mostly a mild childhood disease. It most often affects children between five and nine years old. But the mumps virus can infect adults as well. When it does, complications are more likely to be serious. As more children receive mumps vaccine, it is expected that cases will become more common in older children than in younger ones
Respiratory synctial virus (RSV)
RSV is the single most important cause of severe LRIs in infants and young children. RSV disease spectrum includes a wide array of respiratory symptoms, from rhinitis and otitis media to pneumonia and bronchiolitis, the latter two diseases being associated with substantial morbidity and mortality. Humans are the only known reservoir for RSV. Spread of the virus from contaminated nasal secretions occurs via large respiratory droplets, so close contact with an infected individual or contaminated surface is required for transmission. RSV can persist for several hours on toys or other objects, which explains the high rate of nosocomial RSV infections, particularly in paediatric war
Schistosomiasis
Schistosomiasis, also known as bilharziasis, is second only to malaria in public health importance. It is estimated that 200 million people worldwide are infected with the snail-transmitted, water-borne parasitic helminth, and that 20 000 deaths are associated with the severe consequences of infection, including bladder cancer or renal failure (Schistosoma haematobium) and liver fibrosis and portal hypertension (S. mansoni). In sub-Saharan Africa where schistosomiasis constitutes an important public health problem, a survey in 2000 of disease-specific mortality reported that 70 million individuals out of 682 million had experienced haematuria and 32 million dysuria associated with S. haematobium infection. It was estimated that 18 million suffered bladder wall pathology and 10 million hydronephrosis. Infection with S. mansoni was estimated to cause diarrhoea in 0.78 million individuals, blood in stool in 4.4 million and hepatomegaly in 8.5 million. Using the very limited data available, mortality rates due to non-functioning kidney (from S. haematobium) and haematemesis (from S. mansoni) have been estimated at 150 000 and 130 000 per year, respectively. Although these are global estimates of the schistosomiasis disease burden, the public health impact of schistosomiasis in the field has been poorly evaluated and is still subject to controversy. Apart from a few situations where schistosomiasis is or was recognized as an obvious public health problem, as in Brazil, China, Egypt, the Philippines, northern Senegal and Uganda, the disease is often not a priority for health authorities. Moreover, the lack of a simple clinical case definition does not enable rapid identification of the disease by health personnel. More
Streptococcus A
Group A streptococci (hemolytic Streptococcus pyogenes) cause a broad spectrum of diseases, ranging from simple and uncomplicated pharyngitis and skin infection to life-threatening invasive illness that includes pneumonia, bacteraemia, necrotizing fasciitis, streptococcal toxic shock syndrome (TSS), and nonsuppurative sequelae such as acute rheumatic fever and glomerulonephritis. Streptococcal pharyngitis continues to be one of the most common childhood illnesses throughout the world. The incidence of rheumatic fever has declined in industrialized countries since the 1950s and now has an annual incidence of around 0.5 cases per 100 000 children of school age. In contrast, it remains an endemic disease in developing countries, with annual incidence rates ranging from 100 to 200 cases per 100 000 school-aged children. It also is a major cause of cardiovascular mortality.
Australia's aboriginal population suffers the highest incidence worldwide. Group A streptococci, S. pneumoniae and Staphylococcus aureus are important causes of severe infection in young children in the Papua New Guinea highlands. It has recently been estimated that there currently are more than 18 million cases of severe group A streptococcal disease such as rheumatic heart disease in the world, with more than 500 000 deaths each year. Prospective, longitudinal studies are clearly needed to better understand the epidemiology of streptococcal infections in developing countries and implement more effective public health prevention programmes
Streptococcus B
Group B streptococci are one of the most important infectious causes of neonatal morbidity and mortality. Women vaginally or rectally colonized with Group B streptococci during pregnancy are at increased risk of transmitting the bacteria to their newborn infant during labour and delivery. Pregnancy-associated streptococcal infection can result in maternal sepsis. It also is the leading cause of chorioamniotitis and one of several infections now thought to enhance the risk of preterm rupture of membranes. In the newborn, early onset of the disease is recognized as pneumonia and bacteraemia within the first seven days of life, whereas late onset disease primarily occurs in the form of meningitis between 7 and 90 days of age. Vaginal group B streptococcal colonization has been reported to occur in about 12–27% of women in North Africa, India, the Middle East, Pakistan, Saudi Arabia and the USA. Surprisingly, a WHO collaborative study on serious infections in young infants conducted in four developing countries showed that Group B streptococci were found in only 2 of 167 blood culture isolates and 1 of 40 CSF isolates, whereas Group A streptococci were recovered from 29/167 blood isolates and 3/40 CSF isolates. These data may have been biased by the fact that infants who develop streptococcal sepsis on the day of birth will usually not survive. It might also be that Group B streptococcal-related morbidity in developing counties often manifests itself through miscarriage or preterm delivery, in which case infants may not survive to develop confirmed sepsis. More
Tetanus
Tetanus is acquired when the spores of the bacterium Clostridium Tetani infect a wound or the umbilical stump. Spores are universally present in the soil. People of all ages can get tetanus but the disease is particularly common and serious in newborn babies ("neonatal tetanus"). It requires treatment in a medical facility, often in a referral hospital. Neonatal tetanus, which is mostly fatal, is particularly common in rural areas where deliveries are at home without adequate sterile procedures. WHO estimated that neonatal tetanus killed about 180 000 babies in 2002.
Tetanus can be prevented through immunization with tetanus-toxoid (TT) -containing vaccines. Neonatal tetanus can be prevented by immunizing women of childbearing age with tetanus toxoid, either during pregnancy or outside of pregnancy. This protects the mother and - through a transfer of tetanus antibodies to the fetus - also her baby. Additionally, clean practices when a mother is delivering a child are also important to prevent neonatal and maternal tetanus. People who recover from tetanus do not have natural immunity and can be infected again and therefore need to be immunized. To be protected throughout life, an individual should receive 3 doses of DTP in infancy, followed by a TT-containing booster at school-entry age (4-7 years), in adolescence (12-15 years), and in early adulthood.
Worldwide, all countries are committed to "elimination" of maternal and neonatal tetanus (MNT), i.e. a reduction of neonatal tetanus incidence to below one case per 1000 live births per year in every district. As of December 2007, 47 countries remain that have not eliminated MNT.
Tick-born Encephalitis
The endemic area for tick-borne encephalitis (TBE) spreads from Alsace-Lorraine in the west to Vladivostok and north-eastern regions of China in the east, and from Scandanavia to Italy, Greece and Crimea in the south. TBE also is endemic in North Japan, where the virus has repeatedly been isolated from blood samples of sentinel dogs, ticks, and rodent spleens. TBE is a serious acute central nervous system infection which may result in death or long-term neurological sequelae in 35–58% of patients. The fatality rate associated with clinical infection is 0.5–20%. The proportion of cases involving subclinical infection varies between 70% and 98%. Symptomatic infection occurs in all age groups.More

Typhoid
Typhoid fever is caused by Salmonella typhi, the typhoid bacillus. It is characterized by the sudden onset of sustained fever, severe headache, nausea, loss of appetite, constipation or sometimes diarrhoea. Severe forms have been described with mental dullness and meningitis. Case-fatality rates of 10% can be reduced to less than 1% with appropriate antibiotic therapy. However, strains resistant to chloramphenicol and other recommended antibiotics (ampicillin, cotrimoxazole and even ciprofloxacin) have become prevalent in several areas of the world. Paratyphoid fever can be caused by any of three serotypes of S. paratyphi A, B and C. It is similar in its symptoms to typhoid fever, but tends to be milder, with a lower fatality rate.
INFECTIOUS DISEASES
Infectious diseases are caused by pathogenic microorganisms, such as bacteria, viruses, parasites or fungi; the diseases can be spread, directly or indirectly, from one person to another. Zoonotic diseases are infectious diseases of animals that can cause disease when to transmitted humans.