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Vaccines
Vaccines
• A vaccine is a biological preparation that provides active acquired immunity to a particular disease.
• Vaccines are typically made of an agent that resembles the disease causing microorganism, or its toxins, or one of its surface proteins.
What are vaccines made of?
• There are several types of vaccines:• Inactivated – a previously virulent microorganism that has been destroyed
with chemicals, heat, radioactivity or antibiotics.
• Examples: Influenza vaccine, bubonic plague
• Attenuated – live, attenuated microorganisms.• Many of these are active viruses that have been cultivated under
conditions to disable their virulent properties, or that are closely related but less dangerous organism that produce a broad immune response.
• Examples: viral – measles, bacterial - typhoid
• Typically produce more durable immunological response, but may not be safe for immunocompromised individuals. (May rarely mutate to a virulent form and cause disease.)
• Toxoid – made from inactivated toxic compounds that cause illness rather than the microorganism.
• Examples: tetanus and diptheria
Subunit – protein subunit
• Rather than introducing a “whole-agent” vaccine, a fragment can be used to create an immune response.
• Example: Hepatitis B virus – only the surface proteins of the virus
Conjugate
• Certain bacteria have polysaccharide outer coats that are not good at causing an immune response.
• But, by linking these outer coats to proteins (e.g. toxins) the immune system can be led to recognize the polysaccharide as a protein antigen.
• Example – Haemophilus influenzae type B vaccine
How the vaccine works
• The agent stimulates the body’s immune system, to produce B memory cells, so that if the immune system encounters these microorganisms in the future it will easily recognize and destroy them.
Schedule
• For the best protection, children are recommended to receive vaccinations as soon as their immune systems are sufficiently developed to respond to the particular vaccines.
• Later on “booster” shots are required to achieve “full immunity”.
History
• Edward Jenner (1700s) learned that dairy workers never got the disease small pox, which was deadly and disfiguring.
• Instead the dairy workers got cowpox, a much milder disease.
• Jenner took pus from the hand of a milkmaid with cowpox and scratched it into the arm of an 8-year-old boy.
• Six weeks later he inoculated (inserted smallpox fluid) the boy with smallpox, but the boy did not catch smallpox.
• Smallpox was eradicated worldwide by the 1960s and 70s. There are no human cases, and smallpox is not found in any other organisms.
• This achievement was hoped to be the first for many disease’s eradication.
Herd Immunity
• The form of immunity that occurs when a significant proportion of the population is vaccinated.
• Provides a measure of protection for individuals who have not developed immunity, such as babies, and immunocompromised individuals.
Are vaccines harmful?
Myth: MMR causes autism
• MMR is a vaccine for mumps measles and rubella given to toddlers.
• Symptoms of autism usually become apparent around the same time as MMR is given – no causality proven.
• Autism probably has multiple components including genetics.
Myths about vaccines
• Myth: Thimerosal causes autism• Thimerosal – is a compound that contains mercury, and was used as a
preservative in vaccines
• There was no evidence of harm, but it has been taken out of vaccines as a precaution
• Thimerosal has not been used in any routinely recommended childhood vaccines since 2001
• Multiple studies have shown that thimerosal in vaccines does not cause autism when comparing children who received thimerosal-containing vaccines and those who received thimerosal free vaccines.
Myth: vaccines contain harmful chemicals
• Vaccines contain aluminum as an adjuvant – an ingredient that improves immune response. This allows for less antigen to be used.
• Aluminum is a very common metal found in nature, and infants get more of it through breast milk than in vaccines.
Continued chemicals
• Formaldehyde – used to detoxify diphtheria and tetanus toxins or to inactivate a virus.
• There is a very small amount left over in the vaccine, but it is safe.
• Humans normally have formaldehyde in their bloodstream at levels higher than found in vaccines.
Myth Vaccines are not effective
• Most childhood vaccines are very effective when properly administered (~80% - 100%), but no vaccine claims to be 100% effective.
• Some adult vaccines are not as effective as childhood vaccines.
Myth: Natural Infection is better than immunization• Natural infection usually does cause better immunity than
vaccination.
• However the price paid for natural disease can include paralysis, permanent brain damage, liver failure, liver cancer, deafness, blindness, pneumonia or death.