Before I retired, I got a bad cold every January – without fail. Sometimes I’m not too smart, and it took some years before I figured out what was going on. I was a teacher, and the students came back to school from all over the country after the holiday break bringing with them a veritable zoo of new viruses. Since I hadn’t been exposed to many of them before, I didn’t have immunity and was susceptible to them. Now, I didn’t come into direct contact with all these returning students, but I was not alone in not having immunity. My colleagues and other students also became infected, which allowed these viruses to rapidly spread. One of the many good things about retirement is that I no longer (knock on wood) have a yearly January cold. What brought this all to mind is the news about serious outbreaks of measles.

The mathematical study of the spread of diseases is very interesting, at least to math nerds like me. It has been found that how fast a disease spreads, or dies out, depends on many factors including how contagious it is, how many are uninfected, how many are immune, and so forth. In particular, crowd immunity is a real thing; once a certain proportion, which depends on the disease, of the population has immunity, it is very difficult for the disease to spread. Hence, when you get a flu shot you are protecting others as much as you are protecting yourself. The recent outbreaks of measles are largely due to the lessening of crowd immunity due to lower vaccination rates. The mathematical models vary from disease to disease, and similar models apply to other populations. Predator-prey models deal with populations like foxes and rabbits. They explain things like the 17-year locust, which only appears in large numbers every 17 years; the long gaps makes it difficult for predators to maintain large populations. Still other models explain competing species situations like the way exotic plant species crowd out native ones in places such as the Everglades.

These kinds of models have even been used to study the spread of ideas or political movements. This makes me curious about what the models describing the rapid spread of Christianity after Pentecost would look like. I’m sure that the Roman roads and the relative stability of their rule played a factor, and its being taken to the previously unexposed gentiles was also important. However, I believe that the contagiousness of its message, the Good News, was the biggest factor. Today many Christians have become discouraged about the state of the Church; for example, congregational memberships are down and fewer people are active Christians. We should keep faith, however. The Gospel is still contagious. The Holy Spirit is still guiding us, God’s grace is still freely given, and His unconditional love is still given for all.

Jim