Higher Human Biology Unit 3 – Neurobiology and Immunology

1. Higher Human Biology Unit 3 – Neurobiology and Immunology Section 23 - Immunisation

2. a) Immunisation We will be learning… • To explain the importance of vaccination • To Describe how vaccination can be used to develop immunity from infectious pathogens • To define that the antigens used in vaccinations can be inactivated pathogen toxins, dead pathogens, parts of pathogens and weakened pathogens. • To state that antigens are usually mixed with an adjuvant when producing the vaccine

3. What is Immunity? This is the body’s defence system against pathogens . This can be broken down into three sections: 1st Line of Defence - Physical and chemical barriers 2nd Line of Defence - Inflammatory Response 3rd Line of Defence - Acquired/Active/Adaptive Immunity B & T Cells Vaccinationrefers to the use of some weakened form of a pathogen, whereas inoculation uses the real thing so is consequently a much more dangerous option.

4. Types of Immunity Immunity may either be active or passive: Active immunity- the development of immunological memory, either as a result of exposure to the pathogen's antigens (naturally acquired) or through exposure to the same antigens in a vaccination (artificially acquired); Passive immunity- the acquisition of antibodies, either naturally across the placenta, from breast milk, or artificially through an injection Of these, only the development of artificial active immunity by means of vaccination programmes is of practical importance.

5. Why is Vaccination Important? Vaccinations trigger your 3rd line of defence by activating B cells to produce antibodies. The vaccine activates your immune system without exposing your body to the disease symptoms. • vaccinations are quick, safe and extremely effective • once a person has been vaccinated against a disease, their body can fight it off better • if a person is not vaccinated, they're at higher risk of catching and becoming very ill from the illness

6. How does a Vaccination Create Immunity? An injection of vaccine containing the antigen can be given to stimulate the development of artificial immunity. Exposure to the antigen induces a primary response from the adaptive immune system, in particular leading to the development of an immunological memory in the form of memory B- and T-lymphocytes.

7. In a second or subsequent exposure to the same antigen, a secondary response is triggered. As soon as the antigen is detected, memory cells begin rapid division to generate large numbers of B-lymphocyte plasma cells. These cells release their antibodies into the circulation, leading to such a quick build up of antibodies that the invading pathogen is neutralised before it can cause any harm. However, while vaccination greatly reduces the chance of infection, it cannot entirely eliminate it.

8. What Antigens can be used in Vaccines? • Live attenuated microbes - these contain the same antigens as the pathogen, but the microbes have been sub-cultured many times in the laboratory so that they become an 'attenuated' strain, i.e. they can no longer cause the full-blown disease, although they may cause a very mild form of it. The first vaccine, the smallpox vaccine, consisted of a live attenuated virus. The MMR (measles, mumps and rubella) vaccine falls into this category. • There are a variety of sources used to provide the essential antigens in a vaccine. • Toxoid - these are inactivated toxins; vaccines include Diphtheria and tetanus • 3. Dead pathogens - the microbes are destroyed by heat and chemicals although the dead pathogen still carries the antigens which stimulate the immune response; vaccines for Hepatitis A, polio and cholera fall into this category. • 4. A fragment of a pathogen - the viral coat component can be used as a vaccine; the HPV vaccine • has the viral protein coat protein of the Human Papilloma Virus, as does the vaccine for Hepatitis B.

9. What can be used for Vaccinations? In addition to the antigenic ingredient, vaccines contain chemicals which act to modify the immune response triggered by the vaccine. These are called an adjuvant. These chemicals either act to increase the production of antibodies or by making the protection provided last longer. The most commonly used adjuvant is alum (potassium aluminium sulphate), although several other substances may be used including paraffin oil and bacterial products.

10. b) Herd Immunity We will be learning… • To define the term herd immunity • To be able to define the importance of herd immunity • To describe how non-immune individuals can be protected by herd immunity • To define the term herd immunity threshold • To explain how herd immunity threshold depends on the type of disease, the effectiveness of the vaccine and the density of the population • To describe what mass vaccination programmes are and why they are important to help establish herd immunity • To describe the difficulties and limitations that can arise when widespread vaccinations are not possible due to poverty in the developing world or rejection based on personal opinion in the developed world.

11. What is Herd Immunity? • The principle of herd immunity applies to control of a variety of contagious diseases, including • influenza, • measles, • mumps, • rotavirus, • pneumococcal disease.

12. Herd Immunity • Vaccines can prevent outbreaks of disease and save lives. • When a critical portion of a community is immunised against a contagious disease, most members of the community are protected against that disease because there is little opportunity for an outbreak. This is because their chance of coming into contact with someone with the disease is minimal.

13. Even those who are not eligible for certain vaccines—such as infants, pregnant women, or immuno-compromised individuals get some protection because the spread of contagious disease is contained. • This is known as “herd immunity"

14. Importance of Herd Immunity • Box 1 shows a community in which no one is immunised and an outbreak occurs. • Box 2, some of the population is immunised but not enough to confer herd immunity. • Box 3, a critical portion of the population is immunized, protecting most community members. Watch the following video on the effect of adverse publicity on the MMR vaccination http://www.youtube.com/watch?v=jfheO9H8CD4

15. Can you be Protected by Herd Immunity If you are not Vaccinated?

16. What is Herd Immunity Threshold? This is the percentage of the population who need to be immunised by the vaccine to offer protection for people who are not vaccinated.

17. What factors affect Herd Immunity Threshold? Some populations do not have herd immunity and this may be because of very different reasons; • In developing countries, malnutrition and poverty prevent mass vaccination programmes • In developed countries, adverse publicity about vaccines leads to parents choosing to not have their child vaccinated.

18. Public Health Mass Immunisation Programmes In most countries, policy in public health medicine is to establish herd immunity to a number of diseases.

19. Public Health Immunisation Programmes

20. Developing Countries Public Health Immunisation Programmes • Difficulties can arise when widespread vaccination is not possible due to • malnutrition and poverty (the developing world), Undernourishment Low access to Health Services Poverty Poor Health Low Productivity

21. Developed Countries Public Health Immunisation Programmes Difficulties carrying out widespread vaccination arise when large numbers of the population reject immunisation programmes. This this is a result of adverse publicity about vaccinations Media attention and consequent public concerns about vaccine safety followed publication of a small case-series of children who developed autism after receipt of the measles-mumps-rubella (MMR) vaccine. Many well-controlled studies performed subsequently found no evidence that MMR vaccine causes autism. However, despite these studies, some parents remain concerned that the MMR vaccine is not safe. http://news.bbc.co.uk/1/hi/health/3041225.stm

22. c) Antigenic Variation We will be learning… • To describe how some pathogens can change their antigens so that memory cells are not effective against them • To explain the role of antigenic variation in influenzaand why this is a major public health problem

23. How do Pathogens Evade the Specific Immune Response? • Just as vertebrates have developed many different defences against pathogens, so pathogens have evolved elaborate strategies to evade these defences. • One way in which an infectious agent can evade immune surveillance is by altering its antigens; this is particularly important for extracellular pathogens, against which the principal defence is the production of antibodies against their surface structures. Pathogens can change their antigens so that antibodies and memory cells are useless. The influenza virus is typical of this, and this is why you need a new ‘flu jag every year.

24. What is Antigenic Variation? • Antigenic variation is a change in surface antigens on an infectious organism to help the organism evade the immune systems of potential hosts. • Organisms use a variety of tactics for changing the composition of the antigens on their surface. • This evolutionary trick allows them to continue growing and spreading in populations, perpetuating their existence. • Antigenic variation is of interest for people in charge of developing vaccines and medications to prevent and treat infection.

25. Antigenic Variation • Organisms like viruses, bacteria, and parasites all have an external envelope, with a series of surface proteins. • When an organism enters a host for the first time, the immune system does not recognize any of the proteins and may allow the organism to multiply, creating an infection. • The immune system will learn that those proteins are dangerous, and when the organism appears in the future, the body will go on the attack. • It sees the proteins, recognizes them as a threat, and sends out immune cells to kill the organism.

26. Antigenic Variation • Without antigenic variation, infectious organisms would quickly become extinct. • Numbers of vulnerable people in the population would drop and the organisms would not be able to survive. • If, however, the organism can change the proteins in future generations, it can adapt and start evading the immune system again.

27. Antigenic Variation • Some organisms experience random mutations, which can occur at any time. • Others actually program in antigenic variation. These organisms can switch proteins on and off to present a completely different antigen to the immune system.

28. Antigenic Variation • Antigenic variation can happen through mutation. • Some organisms are better at it than others. • The influenza viruses are a notorious example; they change so much that people must design a new vaccine every year to inoculate people against the flu.

29. Survive and change Survive and change

31. Public Health Immunisation Programmes • Because of vaccines, small pox is now eradicated globally, polio nearly, and, in countries where children are regularly vaccinated, we don’t worry too much about diphtheria, measles, whooping cough, and rubella. • Vaccination may be the most effective public health intervention of all time— that’s especially true in developing countries, where many families can’t find or afford health care when they get sick. The prevention offered by vaccines can be lifesaving.

32. Tuberculosis This disease is caused by a bacteria called mycobacterium tuberculosis. It is spread through the air from person to person. It is easily put into the air when a person coughs or sneezes. The vaccine was developed over a period of 13 years, from 1908 to 1921, by French bacteriologists Albert Calmette and Camille Guérin

33. Polio This is caused by a virus that is spread through faeces in areas of poor sanitation. It passes into the water or food. Polio is very contagious so can also spread by direct contact.

34. Smallpox This is caused by a virus that is spread through prolonged direct face to face contact.

35. a) Immunisation Now I can….. • Explain the importance of vaccination • Describe how vaccination can be used to develop immunity from infectious pathogens • Define that the antigens used in vaccinations can be inactivated pathogen toxins, dead pathogens, parts of pathogens and weakened pathogens. • State that antigens are usually mixed with an adjuvant when producing the vaccine

36. Now I can….. b) Herd Immunity • Define the term herd immunity • Define the importance of herd immunity • Describe how non-immune individuals can be protected by herd immunity • Define the term herd immunity threshold • Explain how herd immunity threshold depends on the type of disease, the effectiveness of the vaccine and the density of the population • Describe what mass vaccination programmes are and why they are important to help establish herd immunity • Describe the difficulties and limitations that can arise when widespread vaccinations are not possible due to poverty in the developing world or rejection based on personal opinion in the developed world.

37. c) Antigenic Variation Now I can….. • Describe how some pathogens can change their antigens so that memory cells are not effective against them • Explain the role of antigenic variation in influenzaand why this is a major public health problem

38. State the aim of public health immunisation programmes and explain why they may fail to protect non-immunised individuals. (6 marks) • Public health immunisation programmes seek to establish herd immunity to a number of diseases. • Herd immunity occurs when a large percentage of a population are immunised. • This percentage is called the herd immunity threshold. • Non-immune individuals are protected because there is a lower probability they will come into contact with infected individuals. • Difficulties arise when widespread vaccination is not effective because of malnutrition, which weakens the immune system… • …or poverty, which reduces vaccination rates… • …or a vaccine being rejected by a percentage of the population.