We would like to note that the patterns observed in this modelling study may change with different transmission characteristics. A longer latent period, for example, might increase invasion and persistence probabilities. Likewise, if immunity is not lifelong, but individuals can instead return to the susceptible class, the infection might persist for longer periods. While such changes might cause the differences between contact–density functions to be more or less outspoken, we doubt that they would change the key patterns observed in this study.