The original vaccine, as most people are aware, was produced by Jenner in 1798. He noted that milkmaids, who handled beasts with cowpox, were immune to smallpox. He used the fluid from the cowpox vesicles to infect the skin of other humans and so produced immunity to smallpox. The two viruses are very similar in structure and the possibility that cowpox was actually smallpox, which had developed a reduction in virulence in milking beasts, is still in question. Smallpox has been eradicated and there are no residual virus cultures held in laboratories.
Vaccination has worked world-wide. The population, born since the mid 60’s, has not been vaccinated and is sensitive to smallpox. The stocks of smallpox virus have been destroyed. If there is any left it could cause chaos if it were liberated. It could be the Armageddon bug.
We now use the word vaccine, in a different context. It is incorrect to say that one has been vaccinated against a particular disease unless that disease is smallpox. The term used is immunized, even though the substance used to produce that immunity is called a vaccine.
Some diseases affect animals and not humans. Examples are distemper in dogs and rinderpest in cattle. We have a natural immunity to these diseases. Other diseases can be prevented by stimulating the body’s defensive system, either by stimulating the production of antibodies in the blood and tissue fluids, or by stimulating the phagocytic white blood cells to engulf and kill disease organisms. This is done by presenting the defences with organisms which, though alive, are incapable of causing disease, i.e. organisms of reduced virulence. Virulent organisms, which have been killed, can stimulate the body’s immune system and even pieces of virulent organisms can sometimes be used with good results. An example is a live poliomyelitis virus vaccine of reduced virulence which, when taken by mouth, induces immunity to the disease. Killed vaccines are used to immunize against enteric fever but the degree of immunity produced is not as high as it would be if the body had had to overcome a low grade infection. Influenza vaccines are inactivated or broken up pieces of influenza virus, which has been grown in fertilised hen eggs. They are not 100% efficient. Live vaccines are more efficient than dead ones.
Efficient vaccines can be made from toxic substances produced by bacteria. The vaccine against tetanus is not directed at the tetanus organism but at its poisonous secretion. The same applies to the diphtheria toxin. It is the poisonous secretions of these germs which are mainly responsible for causing death
Actual infection and recovery from a disease is probably the best method of producing immunity to that disease, but is not to be advocated. However substances, called adjuvants, can be added to the vaccines to enhance their ability to stimulate the body’s defences. In human vaccines this is usually alum. Other substances are used as adjuvants in veterinary work. It has been suggested that the inclusion of whooping cough vaccine in other vaccines would have an adjuvant effect. Whooping cough vaccine has caused fits and brain damage in some children. Its use as an adjuvant in other vaccines has been blamed for causing the Gulf War syndrome.
All vaccines have contraindications and all are liable to produce adverse effects. Most reactions to injected vaccines occur at the site of injection. However three in every 10,000 children, immunized with the mixed measles, mumps, rubella vaccine, develop fever and/or rashes. Some people believe that the measles vaccine is responsible for an increase in the some cases of Crohn’s disease, and other vaccines, notably hepatitis B vaccine, can cause fatal auto immune disease.
There were papers some time ago describing the immunisation of fish as a standard part of fish husbandry! I wonder if it alters the flavour?