Exploring Bioethics - NIH Office of Science Education - National ...

• While an unvaccinated person’s chances of contracting a diseaseare greatly diminished, the risk is not entirely eliminated. If anunvaccinated child happens to come in contact with a virus, he or sheis vulnerable to the disease. This means that parents who opt out ofvaccinating their children reduce overall community immunity andmay place their own children at risk of contracting an illness.3. Ask students what happened to susceptible people in each round.Note that some susceptible people were protected in Round 2 by highlevels of vaccination in the community even though they took no risksof vaccination themselves.4. Remind students that even though unvaccinated individuals are,of course, more susceptible to the risks of acquiring diseases, thisactivity highlights an important fairness consideration in sharingthe benefits and the risks of vaccines across a wider community.5. Ask students additional questions to deepen and extend thediscussion of the simulation. Possible discussion questions include• What do you think would happen if the number of vaccinatedindividuals was increased or decreased even more?• What does the simulation reveal about protecting the mostvulnerable members of the population—babies too young to bevaccinated and people who don’t have good access to health care?• Are vaccination programs designed to protect the individual, thecommunity, or both?6. Ask students how characteristics of the vaccine and the diseasemight affect community immunity. Tell students that the proportionof people in a community that must be vaccinated for communityimmunity to be effective varies depending on the characteristics of thevaccine and the disease, including mode of transmission, how infectiousthe disease is, and how effective the vaccine is. (See table below.)1234Percentage of Community That Must Be Vaccinated for Community Immunity to WorkDisease Community Immunity ThresholdDiphtheria 85%Measles 83–94%Mumps 75–86%Pertussis 94%Polio 80–86%Rubella 85%Smallpox 85%Sources: Centers for Disease Control and Prevention and the World Health Organization. 2001.Smallpox: Disease, Prevention, and Intervention Training Course. Slide 17. Retrieved August 12,2008, from http://www.bt.cdc.gov/agent/smallpox/training/overview/pdf/eradicationhistory.pdf. NationalNetwork for Immunization Information. 2006. Immunization Issues: Community Immunity. RetrievedAugust 18, 2008, from http://www.immunizationinfo.org/immunization_issues_detail.cfv?id=26.Module 2 2-19NoteIf students bring up the limitationsof the simulation, ask them toname as many limitations as theycan think of. Students may offer arange of answers:• It doesn’t model immunity dueto prior exposure.• Individuals do not recover;they stay sick.• Individuals infect only two people in each round.• It doesn’t model risks of the vaccine.56