Vaccination

Vocabulary Check• Vaccination: conferring immunity to a disease by

injecting an antigen (of attenuated microorganisms or inactivated component) so that the body acquires antibodies prior to potential infection

• Immunization: the injection of a specific antigen, derived from a pathogen, to confer immunity against a disease

• Inoculation: to introduce a microorganism into an environment suitable for its growth

• Attenuated: weakened, with diminished or no ability to cause disease

History of Vaccines• Although it had long been recognized that those

who had a disease once rarely contracted the same disease again, the process of immunization was not widely introduced until 1796 by Edward Jenner.

• Jenner realized that milkmaids who contracted cowpox, a mild disease, rarely got smallpox, a much deadlier disease.

• To test his hypothesis, Jenner inoculated an 8 year old boy with fluid extracted from a cowpox pustule of an infected individual. The boy got a mild infection, but when he was later exposed to smallpox, he remained healthy.

History of Vaccines

• Louis Pasteur later noticed a similar phenomenon with chicken cholera bacterium. Chickens which were inoculated with aged bacteria only got a mild version of the disease, and when inoculated again with fresh bacteria, they were immune. The bacteria had become attenuated.

History of Vaccines

• Since this discovery, many vaccines have been produced. Some of the diseases which are vaccine-preventable are:– Hepatitis A & B– Influenza– Measles– Rabies– Tuberculosis

How Vaccines Work

• Vaccines are injected or administered by mouth. Very new vaccines are available as nasal sprays.

• Vaccines contain antigens to a disease which are inactivated or attenuated, and which stimulate an individual’s immune system to produce antibodies.

How Vaccines Work• Vaccines can be manufactured in several

ways:– from dead or attenuated bacteria– from inactivated viruses– from purified polysaccharides from bacterial cell

walls– from inactivated toxins– from recombinant DNA produced by genetic

engineering

How Vaccines Work

• Antibodies produced in response attack the vaccine antigen, and memory cells persist in the body.

• It is these memory cells that will later prevent infection by the same antigen.

• This is termed active artificial immunity.

Primary vs. Secondary Response

Greatest Vaccine Success Story• Eradication of Smallpox– virus enters throat & respiratory tract,

targeting phagocytes and blood cells–flu-like symptoms, leading to lesions, rash,

scabs, severe scarring (if individual survives) –mortality rate around 30%– transmitted by direct contact with infected

individual

Greatest Vaccine Success Story– in 1950s there were

approximately 50 million cases per year

– in 1967, World Health Organization (WHO) began the Intensified Smallpox Eradication Programme

– strategy: mass vaccinations, followed by intensive surveillance

– 1979 declared smallpox eradicated

Vaccine Side EffectsCommon side effects: • fever• allergies• minor swelling and pain at injection siteRare side effects: • panencephalitis (inflammation of the brain) from

measles vaccine• mutation of attenuated strain to virulent strain• brain damage from unknown cause (Whooping

cough vaccine)

Benefits DangersComplete eradication of diseases (e.g. Smallpox)

Excessive vaccination may reduce the effectiveness of the immune system to respond to new infections

Reduced death rate from diseases (e.g. measles)

Vaccine immunity less effective than natural immunity (e.g. measles)

Reduced long term disabilities (e.g. blindness in rubella babies)

Side effects such as possible autism from MMR vaccine