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Why small groups of vaccine refusers can make large groups of people sick

In recent years, the number of parents in America refusing to vaccination their children has increased. The result is an increased number of outbreaks of diseases like the chickenpox and the measles. One example of this outbreak is the recent chickenpox outbreak at a private school called Waldorf. The vaccine refusal rate is about 19 times higher than the national average. The result is the largest chickenpox epidemic in North Carolina in the past 20 years.

This phenomenon highlights why vaccines work, and how it relates to what we have been learning in class. Epidemics spread not only based on the properties or the contagiousness of the disease but based on the network that they are spreading through. This network is called the contact network. In a contact network, the more people that become effected with the disease the more people end up coming in contact with it. This creates more opportunity for the disease to spread. Vaccines work by reducing the chance of people who come in contact from getting the disease. They do not make it impossible for the disease to spread. However, with more people vaccinated, it makes the disease harder to spread. With less infected nodes, there are less ‘contaminated’ branches. This means that overall, the disease reaches a smaller population and the effect is mitigated. This is why vaccinations are good for the whole population, it prevents people from getting exposed to it.


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November 2018