The spread of false teaching about Jesus

For the lesson, “Practice Genuine Purity” how can you illustrate the spread of yeast if you choose to cover the background passage in Matthew 16? Jesus said false teaching by the Pharisees spreads like yeast used in bread (Matt 16:12). Illustrate the danger of false teaching (particularly what is said about Jesus) using the example of how a virus spreads from one person to another. Perhaps use the story of the flu pandemic of 1918 as a backdrop.