Infectious Diseases - Immunity

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  • Infectious Diseases: Immunity
  • White blood cells / response to infection
  • Immune memory
  • Vaccination
  • Monoclonal antibodies
  • Quiz

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Vaccination and immune memory

Developed by Edward Jenner in 1796, vaccination has made a major contribution to the fight against infectious diseases. It prepares your body's immune system to prevent infections from diseases such as measles, mumps, rubella, polio and tetanus.

When you are vaccinated, you are given the pathogen that causes the disease, or even just some harmless fragments of it. It is safe because it contains pathogens that have been killed or weakened so that they do not cause an infection. Vaccines can sometimes be given by mouth or an injection. Sometimes more than one vaccine is given at the same time. This is the case in the MMR triple vaccine (measles, mumps and rubella) which are contained in a single injection.

How vaccination works

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Your immune system detects the foreign pathogens and mounts a primary immune response against them even though they will not cause an infection. It takes a little time for your lymphocytes to make antibodies against the pathogen and during this time, they also build up a large number of memory lymphocytes. These remain in your body for many years and are constantly ready in case of re-infection with the living pathogen. When this happens, they can quickly produce a large amount of antibodies and kill off the infection before any symptoms are seen. You have an immunity against the disease.

With some vaccinations, the immune memory can reduce over several years. Infections like tetanus may need booster vaccinations over a period of time to refresh the memory lymphocytes.

Each vaccination provides immunity against that particular disease and so a programme of vaccinations is given to provide immunity against a range of common infections. The introduction of vaccines has changed the occurrence of disease around the world. Smallpox has gone completely, and polio only remains in a tiny handful of countries. Diseases like diphtheria which used to kill thousands each year in the UK are now almost unheard of. Diseases such as whooping cough are rare. Once a successful vaccine for a disease becomes available, that disease will no longer occur, or become very rare, wherever the vaccine is used in enough of the population to give herd immunity.

A small child receiving an oral polio vaccine in Ethiopia

A small child receiving an oral polio vaccine in Ethiopia.
Courtesy: WHO/P. Virot©

Vaccine for all infections?

It would be ideal if there was a vaccine for all infectious diseases. Sadly it is not possible in reality, at least with the science we have at the moment.

Some diseases, like influenza and the common cold, are caused by viruses that mutate and change year-by-year. They show different antigens on their surface. A new influenza vaccination needs to be given each year when the new strain of the virus have been identified. The cold virus mutates too quickly for a vaccine to be produced and used.

It is also more difficult to make successful vaccines against some diseases, such as HIV/AIDS, and so research continues into the production and testing of new vaccines.

Vaccine risks and benefits?

The benefits of vaccinations are enormous. In the UK alone millions of people are alive and well because they no longer suffer from smallpox, polio, diphtheria, tetanus or any of the serious and often fatal illnesses which used to kill hundreds of thousands of adults and children every year. In fact, vaccines have been so successful that people often forget just how dreadful all these diseases really were!

HPV vaccine for teenage girls

Posters can inform people about vaccinations

Vaccines, like every medical treatment, have a slight risk linked to them. Like all medicines they are tested at length before they can be used, and they are checked constantly once they are being used.

In spite of all this care, sometimes people suffer from bad reactions. These range from simple things like a sore arm after the injection, a mild fever or a rash to more serious symptoms.

It is very difficult to link an event with a vaccine. For example babies have vaccinations several times during their first year of life - and so by simple coincidence they may well suffer from some symptoms of illness in the few weeks after they have been vaccinated. Naturally parents worry that the vaccination has caused the symptoms - but a real link is only shown very rarely indeed.

Between 1990 and 1995 in the UK, there were 5433 suspected adverse reactions to all the vaccines given to children under 15 years of age – out of around 80 million doses of vaccine – that's 0.00008% of cases. Only a tiny number of those were serious.

When vaccine levels fall…

In the late 1990s a UK doctor caused a scare about the safety of the MMR vaccine against measles, mumps and rubella. He has since been completely discredited and struck off the medical register – but as a result of his bad science, worried parents stopped taking their children for the MMR vaccine, many children became seriously ill and a small number died as a result of measles and mumps. People should perhaps have known better – there was a similar scare story about 20 years earlier.

In the mid-70s Dr John Wilson published a report based on 36 patients suggesting that the pertussis (whooping cough) vaccine might cause brain damage in some children. The media publicised the story and parents began to panic. The number of children being vaccinated against whooping cough fell from over 80% to below 50%.

Unfortunately, in their fear of the vaccine people forgot that whooping cough itself causes both brain damage and death. In Scotland alone about 100 000 children suffered from whooping cough between 1977 and 1991 - and about 75 of them died. The same thing was seen across the UK.

whooping cough

Whooping cough can cause brain damage and even kill.
Courtesy of CDC

When the original research was investigated, it was found to have serious flaws. Identical twin girls who were included in the study, and who later died of a rare genetic disorder, had never actually had the whooping cough vaccine! Only 12 of the children investigated had shown any symptoms close to the time of their pertussis vaccine, and the parents were involved in claims for financial compensation from the vaccine manufacturers.

The judge who heard all the evidence in the compensation claims was convinced that the risks of whooping cough far outweighed any possible damage caused by the vaccine, and he severely criticised both the scientist and the study. However the media were not very interested in this part of the story. It was 20 years before vaccination levels, and therefore levels of whooping cough, returned to the levels before the scare. Vaccination uptake is now well over 90%, and deaths from whooping cough are almost unknown in the UK.

 Whooping cough figures and vaccination levels following the scare

Whooping cough figures and vaccination levels following the scare

Medicine that acts against bacterial infections. Penicillin is an example of an antibiotic.
Protein that is produced by lymphocytes (white blood cells) and that attaches to a specific antigen.
Molecule on the surface of a pathogen that identifies it as a foreign invader to the immune system.
Single-celled organism. Has a cell wall, cell membrane, cytoplasm. Its DNA is loosely-coiled in the cytoplasm and there is no distinct nucleus.
The use of biological organisms or enzymes to create, break down or transform a material
To cut apart, or separate, tissue especially for anatomical study.
Exponential growth
If something is growing exponentially the larger the quantity gets, the faster it grows
Micro-organism that can grow in long tubes called hyphae or as single cells. Fungi have a nucleus, cytoplasm and a cell wall.
Herd immunity
If a high percentage of a population is immune to a disease the disease cannot be passed on because it cannot find new hosts.
Infection caused by the human immune deficiency virus (HIV). It attacks and destroys the immune system.
Hybridoma cells are formed by fusing a specific antibody-producing cell with a type of cancer cell that grows well in tissue culture
Immune system
The body's natural defence mechanism against infectious diseases.
A process which gives immune resistance to a particular disease. The human or animal is exposed to a harmless antigen in order to raise antibodies and provide an immune memory.
A type of white blood cell that make antibodies to fight off infections.
A type of white blood cell that consumes dead pathogens that have been killed by antibodies.
Organism that feeds off another living host and causes it some damage. An example of a parasite is a tapeworm that lives in the digestive system of a host organism.
A micro-organism that causes disease.
Phagocytes are the white blood cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells.
A polymer made up of amino acids joined by peptide bonds. The amino acids present and the order in which they occur vary from one protein to another.
Protozoa are one-celled animals
A spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavourable conditions.
A poisonous or toxic substance - produced by pathogens.
A small amount of dead or weakened pathogen is introduced into the body. It prepares the immune system to prevent future infections with the live pathogen.
Medicine that contains a dead or weakened pathogen. It stimulates the immune system so that the vaccinated person has an immunity against that particular disease.
The smallest of living organisms. Viruses are made up of a ball of protein that contains a small amount of the virus DNA. They can only reproduce after they have infected a host cell.
HCG stands for human chorionic gonadotrophin it is a hormone produced by the developing embryo.