A recent report by the American Medical Association warns that the number of parents opting not to vaccinate their children is leading to an increase in outbreaks of preventable infectious diseases. They cite recent measles outbreaks around the United States. Apparently most of the children infected had not been vaccinated against the disease.
Vaccinations work on two levels: they protect the individuals that receive the vaccines and they protect others in the community by decreasing the number of individuals in a community who are susceptible to a disease. In theory, if a large enough percentage of a group is vaccinated, there is a really low chance that the un-vaccinated individuals will be exposed to the disease, creating group immunity. This provides the reasoning behind allowing parents with particular "religious" beliefs to opt out of vaccinating their children. As long as the majority of a population is immune to a disease, the rest of the population is also protected. The problem comes when there is no longer a critical number of people being vaccinated.
My first thought was that an increasing number of parents must be choosing not to vaccinate their children. There have been a lot of stories about the dangers of vaccines so perhaps these are scaring parents away. Then I saw at 2004 report from the CDC that the number of children being vaccinated is increasing. While that is a few years old, perhaps the overall percentage of children is not the problem. Perhaps the recent outbreaks have more to do with the distribution and connectivity of the susceptibles than their number.
Even if the number of parents who choose not to vaccinate their children is a fairly small percentage of the total population, they are likely not distributed evenly. Certain beliefs are likely to be clustered in certain geographic areas which may lead to a clustering of susceptible individuals. The availability of health care will likely leave some populations more vaccinated than others. Siblings of susceptible children and likely to also be susceptible. Additionally, one parent who doesn't believe in vaccinating their children may convince other parents that vaccination is unnecessary, leading to the growth of an un-vaccinated and highly susceptible cluster.
The AMA study states that many of the current measles outbreaks are linked to international travel. Some parents may be lulled into a sense of security by the fact that most of these diseases are very rare in the United States and so the chance that their children being exposed seems really small. However, it only takes one individual to serve as a connection between an infected group and a susceptible group. According to the small world theory, these diseases are likely far closer than we would like to believe.
While the small world theory suggests that we are all closely connected, clusters with similar beliefs are likely more closely connected than other clusters within the population. For example, parents who choose not to vaccinate their children may also tend to send their children to the same types of schools or summer camps, attend similar events and choose similar vacation destinations. All of this conspires to create well connected clusters of un-vaccinated individuals. While only a small percentage of the population may be included, the infection of any one of the individuals could lead to a large outbreak among the susceptible clusters.
There is an interesting dynamic of self defeating, infectious nodes within a larger network of the population. If you picture a network of people in the United States and their daily social connections, most of the individuals are vaccinated from these diseases. There are some individuals scattered throughout the population that remain susceptible but since they are far out numbed by immune individuals, the population as a whole remains immune. Now, imagine that from each of the susceptible nodes spreads the infectious belief of not vaccinating their children. Over time, clusters of susceptibles will form. Perhaps if disease appears in one cluster, the rest of the cluster will again be convinced to vaccinate their children. There must be a fine balance between the infection rate of disease and the popularity of not vaccinating children. Perhaps it is an ongoing cycle: the more distant the disease seems to be, the more contagious the practice of not vaccinating, the more susceptible the population becomes until it becomes infected, then the popularity of the vaccine increases until the disease once again seems distant. This creates interesting challenges of convincing parents to vaccinate their children even when the threat of disease seems so minimal.
Vaccinations work on two levels: they protect the individuals that receive the vaccines and they protect others in the community by decreasing the number of individuals in a community who are susceptible to a disease. In theory, if a large enough percentage of a group is vaccinated, there is a really low chance that the un-vaccinated individuals will be exposed to the disease, creating group immunity. This provides the reasoning behind allowing parents with particular "religious" beliefs to opt out of vaccinating their children. As long as the majority of a population is immune to a disease, the rest of the population is also protected. The problem comes when there is no longer a critical number of people being vaccinated.
My first thought was that an increasing number of parents must be choosing not to vaccinate their children. There have been a lot of stories about the dangers of vaccines so perhaps these are scaring parents away. Then I saw at 2004 report from the CDC that the number of children being vaccinated is increasing. While that is a few years old, perhaps the overall percentage of children is not the problem. Perhaps the recent outbreaks have more to do with the distribution and connectivity of the susceptibles than their number.
Even if the number of parents who choose not to vaccinate their children is a fairly small percentage of the total population, they are likely not distributed evenly. Certain beliefs are likely to be clustered in certain geographic areas which may lead to a clustering of susceptible individuals. The availability of health care will likely leave some populations more vaccinated than others. Siblings of susceptible children and likely to also be susceptible. Additionally, one parent who doesn't believe in vaccinating their children may convince other parents that vaccination is unnecessary, leading to the growth of an un-vaccinated and highly susceptible cluster.
The AMA study states that many of the current measles outbreaks are linked to international travel. Some parents may be lulled into a sense of security by the fact that most of these diseases are very rare in the United States and so the chance that their children being exposed seems really small. However, it only takes one individual to serve as a connection between an infected group and a susceptible group. According to the small world theory, these diseases are likely far closer than we would like to believe.
While the small world theory suggests that we are all closely connected, clusters with similar beliefs are likely more closely connected than other clusters within the population. For example, parents who choose not to vaccinate their children may also tend to send their children to the same types of schools or summer camps, attend similar events and choose similar vacation destinations. All of this conspires to create well connected clusters of un-vaccinated individuals. While only a small percentage of the population may be included, the infection of any one of the individuals could lead to a large outbreak among the susceptible clusters.
There is an interesting dynamic of self defeating, infectious nodes within a larger network of the population. If you picture a network of people in the United States and their daily social connections, most of the individuals are vaccinated from these diseases. There are some individuals scattered throughout the population that remain susceptible but since they are far out numbed by immune individuals, the population as a whole remains immune. Now, imagine that from each of the susceptible nodes spreads the infectious belief of not vaccinating their children. Over time, clusters of susceptibles will form. Perhaps if disease appears in one cluster, the rest of the cluster will again be convinced to vaccinate their children. There must be a fine balance between the infection rate of disease and the popularity of not vaccinating children. Perhaps it is an ongoing cycle: the more distant the disease seems to be, the more contagious the practice of not vaccinating, the more susceptible the population becomes until it becomes infected, then the popularity of the vaccine increases until the disease once again seems distant. This creates interesting challenges of convincing parents to vaccinate their children even when the threat of disease seems so minimal.
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3 comments:
This is a fascinating topic. I would love to see classes in public health taught at COA. It would be an ideal forum for exploring phenomena that are profoundly interdisciplinary, incorporating perspectives from medicine, psychology, economics, politics, history, math, and computer science. And probably more. Thanks for a great post, cecily.
The idea of clusters forming to make pockets of unvaccinated people is an interesting one. It defiantly seems logical to me that people with the same ideals might tend to congregate. Another question that could be interesting is whether or not the clusters are well connected to other clusters. If the clusters are relatively unconnected then it does not seem likely that the disease would spread very far or affect many people overall. However if a large number of the unvaccinated people ascribed to the same religion or other group it may be more likely that the clusters are more closely connected leading to an increase in disease. Anyway those are just some thoughts.
This is pretty interesting in light of an MPBN story I've been following. Apparently due to budget constraints, as of January 1, Maine will no longer provide immunizations to all children in the state - only to children whose parents' income is below a certain threshold and/or are uninsured...It seems like this, combined with parent's reservations about the benefits of immunization, means that Maine might soon be a good case study for unvaccinated clusters of children...
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