Sunday, May 04, 2008

More on the free-rider problem

Vaccine rejectionism involves three all too human tendencies: fundamental misunderstanding of scientific principles, irrational risk perception, and selfishness. Vaccine rejectionists lack even the most basic understanding of immunology and epidemiology. Vaccine rejectionists have no concept of risk. They grossly overinflate the risk of vaccine complications and grossly underestimate the risks of vaccine preventable diseases. What is particularly ironic about vaccine rejectionism is that parents who are busily congratulating themselves on avoiding the risks associated with vaccines are doing so by being free-riders and taking advantage of everyone else.

Thomas May, a bioethicist, has written an excellent exposition of the free-rider problem in the article Public Communication, Risk Perception, and the Viability of Preventive Vaccination Against Communicable Diseases. The article appeared in the journal Bioethics in 2005. This article also includes one of the best explanations of vaccination I have read. On the results of vaccination programs:
Since its inception, the program of mandatory childhood vaccination for children entering the U.S. public school system has been remarkably successful – widely recognized as one of (if not the) most successful public health programs in history. The program has resulted in the eradication of smallpox, the elimination of polio, and a radical reduction in the number of cases of diphtheria, measles, pertussis (whooping cough), rubella, mumps, and a number of other serious diseases. For example, diphtheria has dropped from a peak of 206,939 cases in 1921 to only 4 cases in 1990, and similar drops in cases have occurred for measles, mumps, pertussis, and rubella. The success of the childhood vaccination program, however, faces threats from an increasingly visible anti-vaccination movement, and from visible (though extremely rare) cases of adverse reactions to vaccination. The DTP vaccine results in adverse events such as convulsions or shock for 1 in 1,750; acute encephalopathy for 0–10.5 in 1,000,000; and the MMR vaccine results in encephalitis or severe allergic reaction for 1 in 1,000,000. These risks are extremely low when compared to the adverse consequences from contracting vaccinepreventable disease (for pertussis, encephalitis for 1 in 20; death for 1 in 200; for measles, encephalitis for 1 in 2,000; death for 1 in 3,000) ...
On how vaccines work:
No vaccine is 100% effective. The success of vaccination programs relies on a concept known as 'herd immunity,' wherein protection is achieved through attaining a high enough level of immunity to a disease so as to make exposure to the organism that causes the disease extremely unlikely. If a critical mass of people is immune, then, those who are not immune are protected through 'herd immunity'... The actual level of vaccination necessary to maintain herd immunity is different for each potential disease (depending on the rate of effectiveness for the vaccine in question), but generally ranges from 83%–94%.So long as this level of vaccination is attained, those who refuse to be vaccinated are nonetheless protected through the unlikelihood that they will ever be exposed to the disease... If exemptions to vaccination should be great enough to threaten herd immunity, however, significant harms through exposure to vaccine-preventable disease could result not only for those exempted, but for those who are excluded from vaccination for medical reasons, and for those who are vaccinated yet remain susceptible to the disease (since, again, vaccination is not 100% effective).
This is precisely what has happened in the recent measles epidemic. The level of vaccination had decreased to the point where herd immunity was compromised. As a result the children of vaccine rejectionists got measles, as predicted, and children who were too young to be vaccinated got measles as well, also as predicted.

On the logic of free-ridering:
... [T]he action of any one individual will have a nearly imperceptible effect on the achievement of a collective goal, motivating free-riding behavior that seeks to garner the collective good at no cost to the individual in question. This will be true so long as an individual cannot be excluded from the collective good (as exemptors cannot be excluded from the protection provided when herd immunity is achieved), no matter how agreed upon the desirability of the collective good. However, widespread noncompliance with behavior necessary to achieve the collective good can result in loss of the good entirely – even for those who comply – a phenomenon often described as a 'tragedy of the commons.'... [I]ncreases in exemption rates have occurred in several other states, most notably in Utah, where exemptions to mandatory vaccination rose high enough to threaten herd immunity and result in a measles outbreak where half of those contracting measles had been vaccinated but had not achieved immunity (not surprising, since the rate of exemption was roughly equal to the rate of vaccine ineffectiveness).
Vaccine rejectionism is more than a demonstration of ignorance on the part of vaccine rejectionists, and vaccine rejectionism harms others in addition to the children of vaccine rejectionists. Vaccine rejectionism is unethical because vaccine rejectionists implicitly or explicitly seek to enjoy the benefits of vaccination programs without sharing the risks. Vaccine rejectionism is unethical because it harms innocent others who have taken steps to protect themselves. Vaccine rejectionists need to take a closer look at their own behavior. Rather than congratulating themselves on their selfishness, they should be apologizing to the rest of us.


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By Anonymous Anonymous, at 3:55 AM