Key Area 3.7: Immunisation Neurobiology and Immunisation Higher Human Biology for CfE Miss Aitken

Vaccines A vaccine gives a person immunity without causing them to be exposed to a pathogen. It contains a form of the pathogen mixed with an adjuvant This is a chemical which increases the antigenic response, enhancing the immune system Types of vaccines 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 A vaccine gives an individual active immunity against pathogens they may come up against. This immunity has been artificially acquired.

Herd Immunity Vaccines can prevent outbreaks of disease and save lives. When a critical portion of a community is immunized against a contagious disease, most members of the community are protected against that disease because there is little opportunity for an outbreak. Even those who are not eligible for certain vaccines—such as infants, pregnant women, or immunocompromised individuals — get some protection because the spread of contagious disease is contained. This is known as “herd immunity."

Herd Immunity Box 1 shows a community in which no one is immunized and an outbreak occurs. Box 2, some of the population is immunized but not enough to confer herd immunity. Box 3, a critical portion of the population is immunized, protecting most community members.

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

Herd Immunity Herd immunity depends on several things: The type of disease The efficacy (effectiveness) of the vaccine If a disease can show antigenic variation (more later) then a public immunisation programme can be ineffective

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

Public Health Immunisation Programmes Difficulties can arise when widespread vaccination is not possible due to malnutrition and poverty (the developing world),

Developed World 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 eg 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

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.

Evasion Of Specific Immune Response Many pathogens have evolved elaborate strategies to evade the immune system defences. Some pathogens show antigenic variation, which is where they change their antigen every so often to avoid being targeted by antibodies

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 Antigenic variation is of interest for people in charge of developing vaccines and medications to prevent and treat infection.

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.

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.

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. malaria – antigenic variation occurs within a population Trypanosomiasis - Trypanosomes are insect-borne protozoa that replicate in the extracellular tissue spaces of the body and cause sleeping sickness in humans. They select from a range of genes for antigen production