“Public Health Risk Seen as Parents Reject Vaccines” by Jennifer Steinhauer in NYTimes [March 21, 2008] deals with the strategy of vaccination. Specifically, in some cases parents are allowed by the state the choice to either vaccinate or not vaccinate their kids for certain diseases. This problem wonderfully showcases information cascades and network effects.

The article associates parents’ refusal to vaccinate with information cascades. “Alexandra Stewart, director of the Epidemiology of U.S. Immunization Law project at George Washington University, said many of these parents are influenced by misinformation obtained from Web sites that oppose vaccination.” Thus, as more people refuse vaccination, websites pop up and cause even more parents to follow suit. In this way, a few refusers cause a domino effect and directly or indirectly convince many more to do the same. This effect is especially apparent on smaller scales - “There tend to be geographic clusters of ‘exempters’ in certain counties or even neighborhoods or schools. According to a 2006 article in The Journal of The American Medical Association, exemption rates of 15 percent to 18 percent have been found in Ashland, Ore., and Vashon, Wash.”

Network effects also play a role in vaccinations. The more people vaccinate, the more effective the vaccine is because there are fewer carriers of the disease to spread it. The inherent “price” of a vaccination is the real or perceived risk of resultant health detriment. ” ‘When I began to read about vaccines and how they work,’ she said, ‘I saw medical studies, not given to use by the mainstream media, connecting them with neurological disorders, asthma and immunology.’ ” The benefit is the increased immunity to the disease. The parent is willing to vaccinate if the payoff is positive; in other words, if the added immunity overweighs the risks. The article also points out that the Nash equilibrium in this case is not socially optimal. ” ‘I refuse to sacrifice my children for the greater good,’ said Sybil Carlson, whose 6-year-old son goes to school with several of the children hit by the measles outbreak here.” Immunizing her son would increase societal payoff by making the vaccine more effective for everyone, but yet would endanger the child (at least in the eyes of the parent) more than it would potentially help him. Thus, she does what’s best for her child and worse for society as a whole. This is also the case for rational actors in networks with network effects.

Finally, the article deals with popularity. Specifically, experts have found clustering effects whereby parents in a close-knit community make the same choice - to vaccinate or to not vaccinate, as stated in an above quote regarding geographic clusters. As another example, the article gives an example of how an important (”popular”) person or expert can influence his neighbors. ” ‘I do think vaccines help with the public health and helping prevent the occasional fatality,’ said Dr. Bob Sears, the son of the well-known child-care author by the same name, who practices pediatrics in San Clemente. Roughly 20 percent of his patients do not vaccinate, Dr. Sears said, and another 20 percent partially vaccinate. ‘I don’t think it is such a critical public health issue that we should force parents into it,’ Dr. Sears said. ‘I don’t lecture the parents or try to change their mind; if they flat out tell me they understand the risks I feel that I should be very respectful of their decision.’ ” In other words, his complicity in non-vaccination results in a cascade whereby a large fraction of his patients don’t get vaccinated. This subgraph of his patients results in a cluster.

In sum, the game of vaccination versus non-vaccination presents a great case study of game theory, individual benefit versus societal optimality, network effects, and popularity.