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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.