Disease spread and herd immunity (SIR model)

BiologyHealth & DiseaseAges 16–17

The SIR model divides a community into susceptible, infected, and recovered groups. Choose a disease (seasonal flu, COVID-19, measles) with a realistic basic reproduction number R₀, then adjust the vaccination rate and the contact-reduction level (masks, distancing, isolation) to see the epidemic peak drop, arrive later, and the total case count fall – and once the herd-immunity threshold 1 − 1/R₀ is passed, the outbreak cannot take off.