Spotlight: Herd Immunity

When a high percentage of people in a community are vaccinated everyone in the community, including those who have not been vaccinated, is at lower risk of being infected with a potential pathogen. This is known as herd (or community) immunity.

To better grasp how herd immunity works, try these two herd immunity simulators:

• The FRED Measles Epidemic Simulator, developed by the University of Pittsburgh and Carnegie Mellon University, simulates the spread of measles through a population. Users choose a city and state, and watch side-by-side outbreak progressions in the same community. One represents an 80 percent vaccination rate (too low to benefit from herd immunity), and the other represents a 95 percent vaccination rate (high enough to benefit from herd immunity).
• Another herd immunity simulator, developed by Shane Killian and Robert Wood, lets users adjust immunization and infection rates for two groups to simulate various outbreaks. By adjusting the vaccination and infection rates, users are able to see how the spread of a disease can be altered by vaccination. Try programming one side of the chart with a high vaccination rate (.9) and the other with a low rate (.65) and see what happens for yourself!