measles, HIV, brendan nyhan, and an obscure paper I wrote in 2002

Vox has a nice interview with Dartmouth political scientist Brendan Nyhan about vaccine skeptics. What can be done to convince them? Brendan does research on political beliefs and has shown that in experimental settings, people don’t like to change beliefs even when confronted with correct information. His experiments show that this is true not only for political beliefs, but also controversial health beliefs like believing in the vaccine-autism link.

But there was an additional section in the interview that I found extremely interesting. Nyhan notes that it is easier to be a vaccine skeptic when you don’t actually see a lot of disease: “… many of the diseases that vaccines prevent today are essentially invisible in the US. Vaccines are a victim of their own success here.” This reminded me of a 2002 paper I wrote on STD/HIV transmission. In a model worked out by Kirby Schroeder and myself about people proposing to have risky sex with each other, we wrote that the model has an unusual prediction. If people are proposing risky sex based on how often their friends are infected, you may get unexpected outbreaks of disease:

In the models we have presented, there is no replacement; the population is stable. If we allow for replacement, then we arrive at a novel prediction: as uninfected individuals the population (through birth, migration, etc.) and HIV+ individuals leave (through illness), the proportion of infected individuals will decrease. Once this proportion falls, prior beliefs about the proportion of infected individuals will fall, and if this new prior belief is low enough , then HIV- negative individuals will switch from protected to unprotected sex. The long-term effect of replacement in our model, then, is an oscillation of infection rates… There is some evidence that oscillations in infection rates do occur… An intriguing avenue for research would be to link these patterns in infection rates to the behavior depicted in our model.

In other words, if your model of the world assumes that people take risk based on the infection rates of their buddies, then it is entirely possible, even predictable, that you will see sudden spikes or outbreaks because people “let their guard down.” For HIV, as more people use condoms and other measures, people may engage in more risky sex because few of their friends are infected. For measles and other childhood infections, people who live in very safe places may feel free to deviate from the standard practices that create that safety in their first place. I don’t know how to make vaccine skeptics change their minds, but I do know that movements like vaccine skepticism are some what predictable and we can prepare for it.

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Written by fabiorojas

February 9, 2015 at 12:01 am

9 Responses

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  1. I could buy that. It’s a total logical fallacy, but people are always rational.



    February 9, 2015 at 2:05 am

  2. *aren’t*



    February 9, 2015 at 2:06 am

  3. In the spirit of self-citation, I also addressed this issue in print, albeit much more in passing in my 1980 AJS “Selective Incentives” article (Oliver, AJS 85:1356ff).

    Herd immunity is a straightforward collective action problem. There is some risk (cost) associated with the immunization; there is a risk (cost) of getting the disease that is a decreasing function of the number of OTHERS who are immunized; one’s own immunization provides improved (but not perfect) protection against the disease, which is relevant only if there is actually a risk getting the disease. If the level of herd immunity is low, individuals compare the individual protective benefit of the immunization against the risk and ought rationally to prefer the immunization. But if herd immunity is high, the risk of getting the disease is effectively zero, making even a trivial risk or cost of the immunization itself possibly seem too high compared to the benefit. (No, this isn’t in my old article. I’m just laying it out now. But it really is a pretty straightforward collective dilemma problem.)

    The point I was making back in the day (and used immunizations against epidemic diseases as an example) is that you need negative incentives–punishments or sanctions–to enforce cooperation in this kind of case, where near-unanimous cooperation is needed for the collective good.

    Then quoting myself regarding the problem of absorbing the enforcement costs: “But in many circumstances unanimity is not necessary for maximal provision of the public good. This lack of necessary unanimity creates conflicts for the actor who bears the cost of administering the negative selective incentive. Recalling condition (5) for rational use of a selective incentive, the actor using the incentive must compare the likely increase in payoff G(k) from using the incentive with the cost U(k, s) of using the incentive. If G(k) is maximum with some high but nonunanimous level of cooperation (say, 90%), and if the expected number who will cooperate even if there is no negative incentive is above that level, it is irrational to incur the cost of using the incentive, which includes the cost of detecting violators. But nonenforcement of sanctions may lead more actors to prefer defection to cooperation. Declining cooperation threatens the collective good, and the enforcement of sanctions becomes cost effective again. This cycling in the use of negative incentives often occurs in law enforcement and in the provision of public goods such as the immunization of schoolchildren. Depending on the cost functions, it may be entirely rational to enforce sanctions only when noncooperation is high enough to threaten the collective good.” (p. 1369)

    OK, so my quotation is clunky and not quite on. But it does anticipate both the need for actual sanctions and enforcement to prevent epidemic diseases and the problem of cycling in enforcement of those sanctions.



    February 9, 2015 at 4:24 am

  4. OW: First, geniuses think alike. Second, what I take from your paper (and mine) is that there are multiple processes that can “break” herd immunity. Yours is a lack of sanctions, mine is misleading estimates of disease rates in the network. Perhaps if we scour more on this topic, we’d get a better understanding of all the ways that herd immunity can break.



    February 9, 2015 at 4:28 am

  5. OW: PS – self citing is a great way to reveal yourself!



    February 9, 2015 at 4:30 am

  6. If i ever met someone against HIV I would have a discussion with them, get their viewpoint and explain how their risk is a bigger risk to the child. Unfortunately for this discussion I have never met anyone who is against vaccinations.



    February 9, 2015 at 4:41 am

  7. Herd immunity was discovered in populations that had contracted the disease.
    Vaccines were assumed to provide herd immunity.
    This was merely an assumption.

    There’s your jumping off point. Let’s see how well you do changing your beliefs.

    There is another thing: On principle, you shouldn’t be a fascist. Regardless of the efficacy of vaccines. Just like you shouldn’t be a torturer, even if torture “worked” in the sense that somebody actually was “saved” from imminent death. The hypothetical scenarios are raised for the express purpose of helping us ignore the principle.



    February 9, 2015 at 3:18 pm

  8. @August, I don’t think you’re getting what that JID paper is arguing. If anything, it reinforces the need for near-universal vaccination because, indeed, these vaccines are not 100% effective. Herd immunity is the mechanism by which infectious diseases like measles can be eradicated with vaccines having less than 100% effectiveness. Finally, herd immunity wasn’t so much “discovered” as it is a readily-demonstrable consequence of reducing the spread rate of a contagion on a (social) network, in this case via immunization.



    February 11, 2015 at 12:31 am

  9. sexy_science,

    I said it is a jumping off point for any of you interested in figuring out the truth, rather than continuing to repeat the same nonsense. The measles vaccination is not conferring herd immunity, and people who have been vaccinated are getting the disease. There is research to back this up, but people don’t like to change their beliefs and they rather make fun of parents with autistic kids who have, no doubt, been through a lot of hell. Search up more of these author’s papers- especially De Serres.

    Your discussion of herd immunity has a big logic gap in it, because the concept of herd immunity had to preexist the idea to vaccinate everyone in order to achieve herd immunity. Actual herd immunity was discovered among populations in whom most had caught the disease. When vaccines came along, people assumed herd immunity could be achieved with vaccines. What vaccines actually do is keep the age cohort most likely to catch these diseases transiently immune for that time period. The antibodies wane, because, apparently there is a huge difference in immune response to the live disease versus the vaccine.

    Meanwhile, the U.S. is in a dire position because fewer mothers breastfeed and then those who do breastfeed may not have antibodies to pass on to the infants. And people assume the vaccine regime is working, so it isn’t going to occur to them to take extra precautions or start figuring out how to improve their immune system overall so as to withstand the disease.



    February 11, 2015 at 6:07 pm

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