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Immunization Module: Immunity, Vaccines and the Expanded Programme on Immunization

Study Session 1   Immunity, Vaccines and the Expanded Programme on Immunization


In the Communicable Diseases Module, Part 1, Study Sessions 3 and 4, you learned that some diseases are preventable by immunization with vaccines. Many different types of vaccines are available, and these can be enormously successful in preventing some of the major communicable diseases particularly those that affect children if they are used correctly. This Module teaches you about the concepts and procedures required to deliver an effective immunization service in your community. In this first study session, you will learn about how the immune system protects us from infection, the general principles underlying immunization, the types of immunity and the types of vaccines available.

We will also explain the main features of the Expanded Programme on Immunization (EPI) in Ethiopia, and what you as a Health Extension Practitioner can do to help to make it successful. Immunization benefits the whole country because it has the following general outcomes:

  • It prevents millions of people dying needlessly each year.
  • It has led to some diseases being eradicated from the world altogether, for example smallpox, and others are targets for elimination, e.g. polio and neonatal tetanus.
  • It promotes health and optimal growth and development in children.
  • It releases resources for other health interventions.
  • It is an investment for a healthy population and a stronger economy.

Learning Outcomes for Study Session 1

When you have studied this session, you should be able to:

  • 1.1  Define and use correctly all of the key words printed in bold. (SAQs 1.1, 1.2 and 1.3)
  • 1.2  Describe how the human immune system protects the body from infection, and distinguish between the main types of immunity. (SAQs 1.1, 1.2 and 1.3)
  • 1.3  Describe the main general types of vaccines and what they contain. (SAQ 1.3)
  • 1.4  Describe the main features of the Expanded Programme on Immunization (EPI) and how Health Extension Practitioners can help to achieve its strategies. (SAQ 1.4)

1.1  Immunity and the immune system

Immunity is a state in which the body has sufficient defences to be able to resist the development of communicable diseases caused by infectious agents. The main types of infectious agents are bacteria, viruses, fungi, protozoa and parasites. They are also often referred to as pathogens, which means ‘disease-causing organisms’. We will use both terms in this Module.

  • Which of the following are infectious agents: the hepatitis B virus, polio virus, Mycobacterium tuberculosis, Neisseria gonorrhoeae, Candida albicans, Giardia intestinalis, and Plasmodium falciparum?

  • All of these are infectious agents. The list includes two viruses (causing hepatitis and polio), two bacteria (causing tuberculosis and gonorrhoea), a fungus (Candida causes oral and genital thrush), one protozoan (Giardia causes diarrhoea), and one parasite (Plasmodium causes malaria).

The immune system is the name given to the network of cells, proteins, tissues and organs within the body (Figure 1.1), which act together to protect us against infectious agents. In addition to the structures shown in Figure 1.1, the cells of the immune system also circulate in the blood and some of them migrate through the tissues. These cells are usually known as white blood cells, which is a confusing name because they are found throughout the body – not just in the blood. Wherever an infectious agent gets into the body, it will soon be detected and attacked by the immune system.

Figure 1.1  The sites in the body (in addition to the blood) where the cells and molecules of the human immune system are concentrated. (Source: The Open University, SXR376 Preparatory Reading, Figure 1.2)

The immune system of a healthy and well-nourished adult may be able to fight an infection and stop the disease from developing, or reduce it to mild symptoms. But in very young or elderly persons, or people who are malnourished or in bad health – particularly if they already have HIV, TB or malaria – the immune system is not strong enough to protect them from a new infection. They can become very ill and even die without medical treatment.

  • In addition to the immune system, can you think of other ways in which the human body protects itself from infectious agents?

  • Intact skin covering our bodies acts as a barrier preventing entry of infectious agents. You may have also thought of the hairs and mucus inside the nose, which trap bacteria from the air. Coughing and sneezing, vomiting and diarrhoea rids the body of large numbers of infectious agents, but also spreads them to other people.

1.1.1  How does the immune system protect us from infection?

In this section, you will learn about the different ways in which people can acquire immunity (become immune) to infectious agents. Immunity may be non-specific or specific.

Non-specific immunity

Non-specific immunity (also known as innate immunity — ‘innate’ means ‘already formed at birth’) includes protection from infectious agents by mechanical barriers, such as intact skin or the mucus membranes lining the inside of our nose, mouth, lungs, reproductive system and gut. It also includes the actions of some kinds of white blood cells that can engulf (‘eat’) or kill a wide range of infectious agents, without distinguishing between them.

Specific immunity

In this study session, we will focus on specific immunity, which is the type generated by immunization. Specific immunity is produced when the immune system reacts specifically against one particular type of infectious agent in ways that we will now describe.

When bacteria, viruses or other pathogens get into the body, they are identified as ‘foreign’ by special white blood cells in the immune system, known as helper T lymphocytes or helper T cells (Figure 1.2). Infectious agents are recognised as foreign because they have unique proteins — called antigens — on their surfaces, which the helper T cells can detect. Each type of infectious agent has its own unique antigens, so the person’s immune system can tell which type of infectious agent has got into the body, and direct an attack specifically against that pathogen. Some infectious agents release antigens into the body fluids of the organism and the helper T cells detect these too. Thus, a simple definition of an antigen is any substance that is foreign to the organism that is exposed to it, and which the organism’s immune system can detect specifically and attack.

You learned about the family of white blood cells called lymphocytes (pronounced ‘lim-foh-sites’) in the study sessions on HIV/AIDS in Part 3 of the Communicable Diseases Module.

Figure 1.2  Three types of lymphocytes involved in the immune response against infectious agents in the human body. (Diagram: Dr Ignacio Romero)

The surface molecules labelled CD8 and CD4 are unique ‘markers’ of these cells

The helper T cells activate (‘help’) the rest of the immune system to attack the specific infectious agents they have detected in our bodies. In particular, they help two other types of lymphocytes shown in Figure 1.2. The cytotoxic T cells kill our own cells which have become damaged or infected by viruses.

The B lymphocytes or B cells make special proteins called antibodies in response to infectious agents getting into the body. Antibodies are proteins made by B cells, which circulate in the blood or body fluids and attach to the antigens in (or released by) infectious agents. Infectious agents that have antibodies attached to them are neutralised, or destroyed, by the person’s immune system.

The helper T cells also cause the production of long-lived memory cells, which circulate in the body for years, sometimes for the person’s whole life. These cells ‘remember’ that they have met the infectious agent in the past — either during an infection, or through immunization — and they direct a rapid and effective immune attack against it if it ever gets into the body again.

1.1.2  What is immunization?

‘Vaccination’ refers simply to the administration of a vaccine, whereas ‘immunization’ means that the person developed immunity as a result of being vaccinated (or immunized).

The principle in immunization is to introduce a harmless preparation of the antigens from an infectious agent into the body of a person, who becomes immune to the infectious agent as a result. The harmless preparation of antigens is called a vaccine (pronounced ‘vax-een’). It is made from killed or weakened viruses or bacteria, or antigens extracted from the infectious agents. Immunization should happen before the person develops a vaccine-preventable infection, so vaccines are usually given to babies and young children, either by injection or swallowing liquid drops. However, you should note that there are many communicable diseases that cannot be immunized against at the present time, because a suitable vaccine does not yet exist.

  • Can you think of two very important communicable diseases which do not yet have a vaccine?

  • You may have thought of malaria and HIV/AIDS.

1.2  Types of specific immunity

Specific immunity can be naturally or artificially acquired, in both cases through either ‘active’ or ‘passive’ mechanisms. In this section, we will briefly distinguish between these four types of specific immunity.

1.2.1  Naturally acquired immunity

Naturally acquired immunity occurs ‘naturally’ without any intervention from a health professional. The difference between the ‘active’ and the ‘passive’ forms depends on whether the immune person makes the antibodies themselves (actively), or gets them from someone else (passively).

Naturally acquired active immunity

Naturally acquired active immunity occurs after an infection activates the person’s immune system. For example, non-immunized children who develop measles and recover from the illness, get better because they have made an effective immune response against the measles virus. As a result, they acquire protection from measles for the rest of their lives (i.e. they are immune to measles). They have naturally acquired active immunity because the protection developed naturally in their bodies, without a vaccine being given. The immunity is active because the children produced their own antibodies and memory cells, which specifically attack any invading measles viruses they meet in the future.

Naturally acquired passive immunity

Naturally acquired passive immunity occurs when a mother gives her own antibodies to her baby, transferring them from her blood to the fetal blood across the placenta, or giving them to the baby in her breastmilk. The immunity created by these maternal antibodies is naturally acquired from the mother (without any medical intervention). During the first few months of a baby’s life, until the mother stops breastfeeding, her antibodies provide passive protection to the baby against infectious agents that the mother has encountered during her own life. The term ‘passive’ is used because the baby didn’t produce the antibodies itself. The active production of antibodies by the immune system of the baby takes several years to develop properly.

Information about fetal, maternal and placental circulation is given in Box 5.2 in Study Session 5 of the Antenatal Care Module.

Do you know that the tetanus vaccine given to a mother during antenatal care will also protect the newborn infant from tetanus for the first few weeks or months of its life? This is because the maternal antibodies against tetanus bacteria cross the placenta and get into the fetus.

1.2.2  Artificially acquired immunity

In artificially acquired immunity the person must be artificially and intentionally exposed to foreign antigens (actively), or given someone else’s antibodies (passively), in order to generate a protective immune response.

Artificially acquired active immunity

Artificially acquired active immunity is protection produced by intentional exposure of a person to antigens in a vaccine, so as to produce an active and lasting immune response. The antigens in the vaccine stimulate the immune system to produce antibodies and memory cells which are specifically directed against the antigens in the vaccine. After the immunization, if the living infectious agents with the same antigens that were in the vaccine get into the person’s body, the correct antibodies are already present and they bind to the infectious agents. The memory cells generate a rapid immune response from the rest of the immune system, and the infectious agents are quickly attacked and destroyed, often before symptoms of the disease can develop.

Vaccine doses

Some vaccines are given as a single dose, but others are given as a course of three doses at intervals of a few weeks. Some vaccines also require a ‘booster dose’ five to ten years after the original immunization. This is necessary to increase the immune response and ensure an adequate level of protection.

Once established, the protection provided by immunization usually lasts for several years, or even for life. This makes immunization a highly effective method of giving long-lasting immunity.

Artificially acquired passive immunity

Artificially acquired passive immunity is protection acquired by giving a person an injection or transfusion of antibodies made by someone else. These antibodies neutralise the infectious agents in the usual way, but the protection lasts only a few weeks because the antibodies gradually break down and are not replaced. In artificial passive immunization there is no involvement of the person’s own immune system.

1.2.3  Summary of types of specific immunity

Table 1.1 gives a summary of the four different types of specific immunity, with examples to illustrate each of them.

Table 1.1  Summary of different types of specific immunity.
Type of specific immunityExample of how immunity might be acquired
Naturally acquired immunityActiveInfection
PassiveMaternal antibodies crossing the placenta, or in breastmilk
Artificially acquired immunityActiveIntentional exposure to antigens in a vaccine
PassiveInjection or transfusion of someone else’s antibodies
  • You give a polio vaccination containing polio antigens to a baby girl. What type of immunity will the child develop? Explain your answer.

  • The child will develop artificially acquired active immunity. She was deliberately exposed to polio antigens in the vaccine, so her immunity is artificially acquired. She produced her own antibodies and memory cells directed against the polio antigens, so her immunity is active.

1.2.4  Herd immunity

Herd immunity refers to the level of resistance against a specific communicable disease in the community as a whole. When a high proportion of a community is immune to a particular disease that spreads from person to person (e.g. measles), the infectious agents causing that disease find it difficult to infect any non-immune (susceptible) people. This could result in the infection ‘dying out’ in that community, because there are not enough infected people to act as a reservoir for the infectious agents. A high level of herd immunity benefits everyone, because it makes it more difficult for a particular infection to spread from person to person through that community.

  • Suggest two ways in which the level of herd immunity can increase in a community.

  • If a vaccine exists, immunization of a large proportion of community members is the best way to increase their herd immunity. If there is no vaccine, but a large proportion have suffered from a particular infection in the past and recovered from it, herd immunity increases because many people have naturally acquired active immunity (Figure 1.3).

Note that herd immunity is not relevant in communicable diseases where the main reservoir of infectious agents is the environment (e.g. tetanus), or in other animals (e.g. rabies). Susceptible people can still be exposed to these infectious agents, even if herd immunity is very high, because they do not usually spread from person to person.

Figure 1.3  Herd immunity can increase in a community through exposure to infection to a vaccine. (Diagram: Basiro Davey)

The aim of a comprehensive immunization programme is to raise the level of herd immunity so that almost everyone in the population is immune. The immunization coverage rate is the proportion of the population that has been immunized. An immunization coverage rate of over 80% can produce effective herd immunity for some communicable diseases. However, some infectious agents, such as the measles virus, are so easily spread from infected to susceptible people that they require much higher immunization coverage rates — close to 100% — in order to produce effective herd immunity.

1.3  Types of vaccines

Let’s now move on to look at the various types of vaccine. You might have been immunized by injection yourself, or seen children being given immunization by oral drops. What are the differences between these vaccines, and what do they contain?

Vaccines are made from weakened or killed bacteria or viruses, or extracts taken from them, which are intended to produce immunity against a disease. At present, there are no vaccines in the EPI in Ethiopia to prevent infections by fungi, protozoa, parasites or many other important bacterial and viral diseases — but researchers are trying to develop new vaccines, particularly against malaria and HIV. You will learn about the main antibacterial vaccines (which protect against bacterial infections) in Study Session 2 and the main antiviral vaccines (which protect against infections by viruses) in Study Session 3. Here we describe the five general types of vaccine and how they are made safe to use in the human body. They are:

  • live-attenuated vaccines
  • inactivated vaccines
  • sub-unit vaccines
  • recombinant vaccines
  • conjugate vaccines.

1.3.1  Live-attenuated vaccines

Live-attenuated vaccines are prepared from viruses or bacteria that are whole, active and able to cause infection, but they have been weakened in the laboratory. The term ‘attenuated’ (pronounced ‘at-ten-you-ay-ted’) means ‘made weak’, so the infectious agents in the vaccine should cause no disease at all.

Measles vaccine and oral polio vaccine (OPV) are live-attenuated antiviral vaccines. Bacillus of Calmette and Guerin (BCG) is a live attenuated antibacterial vaccine (named after its French inventors) that protects infants and young children against severe forms of tuberculosis (TB).

Live-attenuated vaccines generally activate the immune system very effectively, because they cause a similar reaction in the body as if to a natural infection. For example, a single dose of measles vaccine produces lifelong protection against measles because it is highly immunogenic, i.e. it has a very high ability to produce immunity.

If a mild fever and small rashes appear in a child you have vaccinated against measles, tell the mother not to worry. Reassure her that her child will be protected against the more serious measles disease.

However, live-attenuated vaccines can sometimes produce a weakened disease pattern in a small proportion of vaccinated children. For example, measles vaccines can induce fever and an occasional rash, but this is very unusual and is nothing to worry about. The live-attenuated oral polio vaccine (OPV) can very rarely cause a type of paralysis, but on average this happens in only one child in every 1–10 million vaccinated children.

1.3.2  Inactivated vaccines

The pentavalent vaccine used in the EPI in Ethiopia contains five vaccines and is sometimes referred to as DPT-HepB-Hib vaccine. The letters refer to diphtheria-pertussis-tetanus-hepatitis B-Haemophilus influenzae type b.

Whole-cell inactivated vaccines are produced by first growing viruses or bacteria in the laboratory and then inactivating (killing) them with heat or chemicals. Because they are not alive, they cannot cause the disease. The pertussis component of the pentavalent vaccine used in the EPI in Ethiopia is an example. The whole-cell inactivated version of this vaccine contains the Bordetella pertussis bacteria, which cause whooping cough, but they have been killed so that they are no longer harmful.

  • Even though they cannot cause infection in the immunized person, the infectious agents in an inactivated vaccine are still immunogenic. What does this mean?

  • They are still capable of causing a strong immune reaction in the immunized person, which usually protects him or her from that particular infection in the future.

1.3.3  Sub-unit vaccines

Sub-unit vaccines are made from parts of infectious agents, or certain chemicals produced by bacteria. Because the vaccine does not contain whole organisms, they cannot cause disease in immunized people. The diphtheria and tetanus components of the pentavalent vaccine are of the sub-unit type. Diphtheria and tetanus bacteria each produce special toxins — harmful chemicals that cause the symptoms of these diseases. The pentavalent vaccine contains diphtheria and tetanus toxoids — modified versions of the bacterial toxins, which have been developed in a laboratory. The toxoids don’t cause disease symptoms, but they do stimulate a protective immune response in vaccinated people. A sub-unit version of the pertussis vaccine now exists and is increasingly being used instead of the older whole-cell inactivated version.

1.3.4  Recombinant vaccines

Recombinant vaccines are produced by inserting genetic material from a disease-causing organism into a harmless cell, which then makes lots of copies of the antigens of the infectious agent. The antigens are then purified and used as a vaccine. An example is hepatitis B vaccine (the HepB component of the pentavalent vaccine used in Ethiopia).

1.3.5  Conjugate vaccines

A conjugate vaccine is made by conjugating (joining together by chemical bonds) an antigen from an infectious agent and a large ‘carrier’ protein. The combination makes the antigen more immunogenic than it would be on its own. An example is the Haemophilus influenzae type b (Hib) vaccine included in the pentavalent vaccine in Ethiopia.

Now we turn our attention to how these vaccines are used in Ethiopia.

1.4  The Expanded Programme on Immunization

The Expanded Programme on Immunization (EPI) began in 1974 when the World Health Assembly pledged to ensure that all children in all countries receive life-saving vaccines. Each year, immunization now prevents more than 2.5 million deaths among children worldwide. An additional 2 million lives could be saved if available vaccines reached every child.

Ethiopia started the EPI in 1980 to reduce mortality and morbidity from vaccine-preventable diseases among children and mothers. The immunization coverage rate has been increasing since that time, but not as fast as the original target. The Ethiopian Federal Ministry of Health (FMOH) has prepared a plan to increase the immunization coverage rate to 80% of the population in 90% of the woredas (districts) in the country. Health Extension Practitioners like you can play a major part in the success of this plan.

1.4.1  Vaccine-preventable diseases in the EPI in Ethiopia

The vaccine-preventable diseases included in the EPI in Ethiopia are:

  • tuberculosis (TB)
  • poliomyelitis (polio)
  • diphtheria
  • pertussis (whooping cough)
  • tetanus
  • measles
  • pneumonia and meningitis caused by Haemophilus influenzae type b bacteria
  • liver disease caused by hepatitis B viruses
  • pneumonia and other infections caused by Streptococcus pneumoniae bacteria
  • diarrhoeal diseases caused by rotaviruses (joining the EPI soon).

In order to achieve the EPI objectives, the FMOH has outlined five strategies that are applicable throughout the country (see Box 1.1 on the next page). Next we will examine each of them in turn and consider what you can do to progress these strategies.

Box 1.1  EPI strategies
  • Increase and sustain high immunization coverage rates
  • Increase the quality of immunization services
  • Reduce missed vaccination opportunities and trace defaulters
  • Improve public awareness and community participation in immunization programmes
  • Ensure prompt reporting and improved control of vaccine-preventable diseases.

1.4.2  Increase and sustain high immunization coverage rates

The key to increasing and sustaining high immunization coverage rates is to increase the accessibility of immunization services, particularly by opening more vaccination delivery sites at times when mothers can bring their infants. As you know, many children are not immunized because they live far away from health facilities. These children could be given the opportunity to be vaccinated through establishing outreach services, supported by mobilisation teams going from house-to-house identifying children (and mothers) who need vaccinations.

You might also have seen health workers giving immunizations in your community in well-publicised campaigns that encourage parents to bring children to the kebele office or the Health Post for vaccination. The progress achieved by the Health Extension Workers at one Health Post can be seen in Figure 1.4. Planning and managing your routine immunization activities are described in detail in Study Session 8, and communication for an effective immunization service is in Study Session 9.

Figure 1.4  Increasing immunization coverage rates achieved in one year at Fura Health Post in the Southern Nations, Nationalities and Peoples Region (SNNPR) of Ethiopia. (Photo: Janet Haresnape)

1.4.3  Increase the quality of immunization services

A successful immunization service has to be of high quality. This means that you must use safe injection practices, and all the required vaccines and other supplies must be available in good condition, and on a regular and timely basis. Poor quality vaccines will not prevent illness. Therefore, to improve the EPI, you need to keep the vaccines at the proper temperature, take good care of the injection equipment and ensure reliable vaccine stock control.

In Study Sessions 5–10, you will learn how to introduce and use quality assurance methods to improve the efficiency and quality of the immunization service at your Health Post

You also need to have good interpersonal communication, supportive supervision and skilled manpower to plan and conduct an effective immunization programme. By increasing your skills as a Health Extension Practitioner, you can play an important role in immunizing all the children in your area. Reaching every child should be your goal.

1.4.4  Reduce missed vaccination opportunities and trace defaulters

It is common in Ethiopia to see many children and mothers who have been to a health facility, but have not been immunized. Thus, another important strategy is to reduce missed opportunities and trace defaulters.

Reasons for missed immunizations

It is important that you check whether or not children and mothers are immunized whenever they come into contact with the health service. If they have missed the opportunity of being immunized during their earlier visits, then you should immunize them. You will learn how to give immunizations in Study Session 4.

Sometimes some children are not given the vaccine at the right time because they have a contraindication — a medical reason for not giving the vaccine either temporarily or permanently, such as a serious illness or high-grade fever (38.5ºC or above). Contraindications are described in Study Sessions 2, 3 and 7. However, very few children have genuine reasons for not vaccinating them at all. Immunization should not be missed if the child has a mild illness.

Tracing defaulters

Have you come across children who started the immunization programme, but have not completed the schedule? These children are still at risk of vaccine-preventable diseases. It is therefore essential to keep a proper registration system of vaccinations, and to establish a community network for tracing defaulters — i.e. people who fail to complete a course of immunization or treatment. You will learn about EPI registration and defaulter tracing in Study Session 8 and a system for identifying them in Study Session 10.

1.4.5  Improve public awareness and community participation in immunization programmes

In the EPI, you are expected to improve public awareness through intensive, regular social mobilisation and health education campaigns, in order to:

  • maximise participation of community members in EPI activities
  • increase public demands for immunization and the vitamin A supplements that are routinely given to infants during the immunization programme.

The techniques for involving the whole community are described in the Module on Health Education, Advocacy and Community Mobilisation.

It is very important to involve the whole community, including political and religious leaders, through seminars, public meetings and direct contacts. You should aim to work with and fully utilise women’s groups, youth associations and idirs (self-help associations at village level), so that they support and help to promote the immunization service (see Study Session 9).

1.4.6  Ensure prompt reporting and improved control of vaccine-preventable diseases

Reporting formats for immediately reportable and weekly reportable cases of priority diseases are in Study Session 41 of the Communicable Diseases Module, Part 4.

It is a key part of your role to identify cases of vaccine-preventable diseases, such as measles, polio, neonatal tetanus and bacterial pneumonia and meningitis, and report them to your supervising Health Centre, who will report to the District (woreda) Health Office. Control of these diseases is largely the result of effective immunization campaigns achieving high immunization coverage rates, and the isolation and treatment of people who are infected, to reduce the risk of infection spreading into the susceptible population.

1.5  Your role in achieving the goals of the EPI

Your role as a Health Extension Practitioner is to lead the following activities, based on the national EPI recommendations:

  • Take every opportunity to identify and immunize all eligible children.
  • Ensure all eligible children attending the Health Post are immunized according to the recommended schedules.
  • Make immunization services routinely available at convenient times for mothers, ideally every day.
  • Involve the community in the schedule for outreach immunization sessions, so that you cover the target population within the target period.

There are five key operations that you need to undertake to run an EPI service efficiently and effectively, which are summarised in Box 1.2. You will learn about these key operations in detail in later study sessions in this Module.

Box 1.2  Five key operations for an effective immunization service

  1. Service delivery: involves strategies and activities in giving safe and timely vaccinations.
  2. Logistics: includes delivery of vaccines and necessary equipment to the site of use, transport, management of the ‘cold chain’ and safe waste disposal.
  3. Vaccine supply and quality: includes forecasting of vaccine needs, procurement, monitoring of vaccine usage rates and vaccine safety.
  4. Disease surveillance: involves monitoring of disease incidence, record keeping and reporting (see the Communicable Diseases Module, Study Sessions 39 to 41).
  5. Advocacy and communication: consists of social mobilisation, advocacy, community education on immunization and vaccination programme promotion.

The diagram on the left of Figure 1.5 summarises the five operational components listed in Box 1.2, and the diagram on the right reminds you that in order to achieve them there must also be:

  • sustainable financing
  • management
  • strengthening human and institutional resources.
Figure 1.5  (left) The five key immunization operations, and (right) the three additional requirements for achieving an effective immunization service.

In the next two study sessions, you will learn the details of the antibacterial and antiviral vaccines used in the EPI in Ethiopia.

Summary of Study Session 1

In Study Session 1, you have learned that:

  1. Immunization is beneficial and effective in the prevention of disease, death and disability from vaccine-preventable diseases. Worldwide, more than 2.5 million childhood deaths are prevented by immunization each year.
  2. The vaccine activates the immune system to produce antibodies and memory cells, which identify and attack infectious agents used in making the vaccine if the live organisms get into the body in the future.
  3. Immunity is the state of being resistant to a particular infection; it can be naturally or artificially acquired, either as active or passive immunity.
  4. Immunization of over 80% of the population gives protection to the susceptible population in a community through herd immunity to vaccine-preventable diseases that are transmitted from person to person.
  5. Vaccines can be prepared as live-attenuated or killed (inactivated) vaccines, or as sub-unit, recombinant or conjugate vaccines.
  6. The vaccine-preventable diseases targeted in the Expanded Programme on Immunization (EPI) in Ethiopia are: tuberculosis (TB), poliomyelitis (polio), diphtheria, pertussis (whooping cough), tetanus, measles, pneumonia and meningitis caused by Haemophilus influenzae type b bacteria; pneumonia and other infections caused by Streptococcus pneumoniae bacteria; and hepatitis B diseases of the liver and diarrhoeal disease caused by rotaviruses.
  7. To achieve the objectives of the EPI, you have an important role in implementing the national strategies to increase and sustain high immunization coverage, increase the quality of the immunization service, reduce missed vaccinations and trace defaulters, improve public awareness and community participation in immunization programmes, and ensure prompt reporting and improved control of vaccine-preventable diseases.
  8. Immunization activities consist of five key operational components: service delivery, logistics, vaccine supply and quality, disease surveillance, advocacy and communication. In addition, sustainable financing, effective management and strong human and institutional resources are also required.

Self-Assessment Questions for Study Session 1

Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering these questions. Write your answers in your Study Diary and discuss them with your Tutor at the next Study Support Meeting. You can check your answers with the Notes on the Self-Assessment Questions at the end of this Module.

SAQ 1.1 (tests Learning Outcomes 1.1 and 1.2)

When the immunization coverage rate is high, the herd immunity of a community is increased. Explain what this means and how everyone in the community benefits from it — including people who are not immune — in the case of a disease like measles, which is transmitted from person to person.


When the immunization coverage rate is high, a large proportion of the members of a community will be immune to the disease caused by the particular infectious agent in the vaccine. This is called herd immunity. Therefore, in a disease like measles, which is transmitted from person to person, there will be a very small reservoir of infection restricted to a few infected people in the community. Transmission of infection from infected to susceptible people will very rarely occur, so the infectious agent will not be able to spread through that community and it may even ‘die out’. This protects the susceptible people even though they are not immune.

SAQ 1.2 (tests Learning Outcomes 1.1 and 1.2)

You see a breastfed baby who appears to be immune to measles, even though he has not been vaccinated. His older brother has measles, but the baby has not developed the illness. How can this happen, and what is this type of immunity called?


Some immunity can be acquired without vaccination. This infant has become temporarily immune to measles because he has received maternal antibodies in his mother’s breastmilk (and possibly also across the placenta before he was born). This type of immunity is called naturally acquired passive immunity (‘passive’ because the antibodies protecting the baby were made by his mother, not by his own immune system).

SAQ 1.3 (tests Learning Outcomes 1.1, 1.2 and 1.3)

  • a.What type of vaccine is the diphtheria component of the pentavalent vaccine?
  • b.Explain how immunization with the pentavalent vaccine gives protection from diphtheria.
  • c.What is this type of immunity called?
  • a.The diphtheria component of the pentavalent vaccine is made from the toxin (poison) produced by the bacteria that cause the disease; the modified toxin is called diphtheria toxoid. This is an example of a sub-unit vaccine.
  • b.The diphtheria toxoid in the vaccine has antigens in its structure which are unique to the diphtheria bacteria. Helper T cells in the immune system of the immunized person recognise these antigens as foreign. They activate other parts of the immune system to make antibodies and memory cells, which remain circulating in the body for a long time. If live diphtheria bacteria get into the body, the person’s immune system is already prepared to attack them and prevent the disease from developing.
  • c.This type of immunity is called artificially acquired active immunity, where a vaccine is used to develop active immunity against an infection (‘active’ because the antibodies and memory cells were made by the person’s own immune system).

SAQ 1.4 (tests Learning Outcome 1.4)

The EPI was started many years ago, but it did not reach its original target of increasing the immunization coverage rate by 10% every year. The EPI has drawn up strategies to improve the immunization service in Ethiopia. How can you help to implement these strategies?


There are many ways in which you can help to implement the EPI services. You may have thought of the following:

  • Help to increase immunization coverage rates by using every opportunity to immunize eligible children, for example, when they are brought to the Health Post for another reason; and by making immunization routinely available at convenient times, preferably on a daily basis.
  • Ensuring the community is made aware of when immunizations are available. Use any strategies you can to sustain high immunization coverage, e.g. reminders, posters, meetings, etc.
  • Increase the quality of immunization services through good management, stock control and safe storage of vaccines and other supplies, and using safe injection practices and disposal of waste.
  • Help to reduce missed opportunities for immunization by checking if all eligible children that you see are immunized, and tracing defaulters (children who have not completed all the vaccinations in the schedule).
  • Help to improve public awareness and community participation in the immunization service by involving community leaders and groups in planning outreach sessions, so as to cover as much of the target population as possible.
  • Keep an accurate register of immunizations and report any cases of vaccine-preventable diseases to the District Health Office.