Active immunity and vaccination What is immunisation? The process by which a person develops immunity to a disease causing organism. i.e. the blood contains memory T and B lymphocytes as well as antibodies able to recognise an antigen from that organism. How can we safely develop active immunity? By vaccination, i.e. exposure to harmless antigens from the pathogen.

How can we safely develop active immunity? By vaccination, i.e. exposure to harmless antigens from infectious pathogen. Where do the antigen come from? – inactivated pathogen toxins – dead pathogens – parts of pathogens – weakened pathogens. How can vaccine efficiency by improved? By mixing them with an adjuvant to enhance the immune response. (adjuvant is a substance that modifies the effect of another agent, in this case, boosts immune response) Vaccines for active immunity

For info only Suitable examples of antigens include: inactivated pathogen toxins (tetanus and diphtheria) dead pathogens (polio and hepatitis A) parts of pathogens (HPV and hepatitis B) weakened pathogens (measles, mumps and rubella).

Vaccines and clinical trials Why are vaccines subjected to clinical trials in the same way as other medicines? to establish their safety and efficacy before being licensed for use Vaccine clinical trial are designed with following which protocols? Randomised Double-blind Placebo-controlled

How is a clinical trial randomised? Subjects are split into groups, generation of a randomization usually includes obtaining the random numbers and assigning random numbers to each subject or treatment conditions. How is a clinical trial made double blind? Neither the subjects nor the researchers know which group they are in. Why is it important to designed a randomised /double blind study? To eliminate bias

How is a placebo protocol set-up in a clinical trial? One group of subjects receives the vaccine, while the second group receives a placebo control (i.e. pile identical in appearance but does not contain the active agents of the vaccine) Why is placebo control included in clinical trials? To ensure valid comparisons. How can the magnitude of experimental error be reduced? Use a suitable size of sample At the end of the trial, how are the final results processed before a conclusion can be drawn? Results from the two groups are compared to determine whether there are any statistically significant differences between the groups. Why do we do statistical analysis? Otherwise, we have nothing to support the conclusion that a difference is significant, i.e. not due to chance.

What is the name given to the fact that when a large percentage of a population are immunised, non-immune individuals are protected as there is a lower probability they will come into contact with infected individuals? Herd immunity

What is meant by herd immunity threshold? When a critical proportion of the population becomes immune, called the herd immunity threshold, the disease may no longer persist in the population, ceasing to be endemic.endemic

Why is reaching herd immunity threshold so important? This herd immunity is important in reducing the spread of diseases and in protecting vulnerable and non-vaccinated individuals.

What is herd immunity threshold depending on? The disease The efficacy of the vaccine The contact parameters for the population

Extra info: Herd immunity was used for the eradication of smallpox in smallpox Herd immunity does not apply to all diseases, just those that are contagious, meaning that they can be transmitted from one individual to another. Tetanus, for example, is infectious but not contagious, so herd immunity does not apply.contagiousTetanus

In most countries, policy in public health medicine is to establish herd immunity to a number of diseases. So why have we not achieved this both in the developing and the developed world? Developing world: Difficulties can arise when widespread vaccination is not possible due to malnutrition and poverty. Developed world: When vaccines are rejected by a percentage of the population.

Evasion of specific immune responses by pathogens Many pathogens have evolved mechanisms that evade the specific immune system which has consequences for vaccination strategies. What are the two main processes responsible for evasion? Antigenic variation Direct attack on the immune system.

Antigenic variation What is meant by antigenic variation? Some pathogens can change their antigens avoiding the effect of immunological memory. Give three examples of such pathogens: - malaria - trypanosomiasis (Sleeping sickness) - influenza

What are the problems caused by antigenic variation? Some diseases are still very common in some parts of the world, e.g. malaria and trypanosomiasis Some diseases remains a major public health problem and risk individuals require to be vaccinated every year, e.g. influenza

Direct attacks to the immune system Give 2 examples of pathogens that directly attack the immune system: - HIV attacks lymphocytes which is the major cause of AIDS (Acquired Immuno Deficiency Syndrom) - Tuberculosis (TB) survives within phagocytes and avoids immune detection.