The New Hatred.

Let me say this at the outset: I am an infectious disease epidemiologist. I believe vaccines represent arguably the most astonishing advance in health that we have yet developed. The lives they have saved are probably literally countless, and the cost at which they have done it is negligible. Vaccines in general are very cheap, very effective, and very safe. I hope, fervently, for a new vaccine for tuberculosis and any vaccine at all for hepatitis C virus. Without them, eliminating either of these diseases will be an uphill battle.

And I have very little time or patience for the endless ridicule and hatred that is heaped upon people who don’t want to vaccinate their children.

I understand that many parents of children who cannot be vaccinated would be furious at the people putting their children at risk, but they would seem to be in a minority among people who pillory anti-vaxxers. It seems to me that anti-vaxxers have now taken the place of young-earth creationists in the New Atheist pantheon of demons to be vanquished.

Vaccination is complex. When it is contentious it involves conflicts between the rights, values and safety of a number of parties; the child eligible for vaccination, its parents, other children, their parents, and the state. These are not simple conflicts to resolve, because the issues are not simply empirical, as many critics appear to believe. Being vaccinated is a medical procedure. It carries risks, although not the ones Andrew Wakefield would have us believe. It requires the consent of someone responsible, and our societies have vested parents, rather than the state, with this responsibility. In communities with low vaccination coverage, vaccinating your child is (in most cases) accepting a small personal risk in exchange for a large potential benefit, but in communities with high coverage, this balance shifts. Risk perception matters, and it is not entirely amenable to rational persuasion.

To take an example relevant to adults: the risk of transmission of HIV during heterosexual sex with somebody whose viral load is suppressed by anti-retrovirals, and with whom one is using condoms, is negligible (and in fact, the per act transmission for heterosexual sex even with somebody who is not on treatment is only around 1 in 1,000). An argument could be made that, depending on one’s social circles, picking up a random stranger of unknown status at a bar actually carries a higher risk than sleeping with someone whose status is known, but whose viral load is confirmed to be low. I could demonstrate this to you. And yet many people would have to think very, very seriously about having sex with someone they knew to be HIV+, if they didn’t simply dismiss it out of hand. I know the odds, and even I don’t know that I could get over my fear. There is more to the question than the facts.

The expectation that people who are afraid of vaccinating their children simply need to read the research and come around fundamentally misunderstands how people change their minds about things they fear. And the idea that anybody – anybody – could be convinced of anything by being vilified as a dangerous lunatic or a complete moron is simply breath-taking. Deciding what constitutes tinfoil-hattery in a world in which Thalidomide and Vioxx happened is not straightforward, and the sad fact is that a lot people who don’t study science after high school find it really, really difficult to assess the credibility of different sources and understand their content. I have two medical science degrees and I can’t manage most Wikipedia chemistry pages. We need to cut people some slack.

It’s easy to say “vaccines work”. Overwhelmingly, they do. But the people who question this are not trying to kill kids. Some of them are afraid. Some of them are paranoid. And yes, some of them are shameless liars. I suspect, although I don’t know, that the former are at least as numerous, if not far more numerous than the latter. They need to be convinced, and they will not be convinced by vilification. Some of them, tragically, will be convinced by whooping cough.

I have no idea how to resolve the conflict between the state, children and public health on one hand, and the adults who will not be convinced on the other. For measles vaccines, in particular, to be effective, coverage needs to be over 95%. But pushing people who are already on the fringe even further out of society cannot be the answer. Even from an epidemiological perspective, if the welfare of children is paramount, creating the conditions under which unvaccinated children can only attend Steiner schools in Byron Bay is the worst possible idea. The Royal Children’s Hospital runs an advisory service for parents who are concerned about vaccination, where they can sit down and talk to a nurse about their fears. Some will be convinced. Some won’t. But I’m alright at statistics, and I know who I’d bet on out of those nurses vs. Penn and fucking Teller.

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4 Responses to The New Hatred.

  1. Cynthia says:

    I came across your post on Twitter and I’m surprised there aren’t any comments here. Maybe people understand science much better than I do.

    The part I’m confused about is where you say, “the per act transmission for heterosexual sex even with somebody who is not on treatment is only around 1 in 1,000.”

    I understood that to mean that having heterosexual sex with someone who is known to be HIV+ positive but “not on [anti-viral] treatment is 1/1000”, which sounds very low. (Why else would you say they weren’t on treatment unless they were HIV+? People who test negative are not on treatment and I’m guessing the transmission rate is less than 1/1000). Am I misreading the sentence?

    If the transmission with a known HIV+ person is 1/1000, how does that compare to the risk of transmission for a random stranger of unknown status (let’s only consider people in the U.S.)?


    • 80% Power says:

      It is indeed a lot lower than most people assume, although that number is an average. The actual risk in any given act depend on the person’s stage of infection, whether the non-infected partner is male or female, what type of sex you’re having, etc.

      The broad things that determine the actual level of risk in a random stranger, unknown status scenario are as follows:

      1) The risk that the person you’re hooking up with has HIV (this varies dramatically within the US by geography and demographics, the risk among young people in Baltimore or middle aged men in San Francisco is much higher than the risk among old people in rural Minnesota, for instance).

      2) If they do have HIV, whether they acquired it recently (again, this risk will be higher in higher-transmission communities) or are in an advanced stage of infection, vs. if they acquired it a moderate time ago and their viral load is low.

      3) The type of sex you have – what kind of penetration occurs, whether you use condoms, etc.

      There are circumstances under which all of these risks with a random stranger might be quite high. If you sleep with a random stranger who doesn’t know their own status, there’s a chance they might have recently acquired HIV, meaning they would be highly infectious, and because neither of you were aware of this you might engage in high-risk behaviour that you otherwise wouldn’t. Let’s say you pick up someone from a high risk group in a high prevalence part of the country, so there’s a 1 in 50 chance they have HIV. Because you don’t realise this, you might not use a condom, so the risk of you getting HIV during the encounter would be 1,000 (so now we’re at about 1 in 50,000; the risk they have HIV multiplied by the risk they’ll pass it to you on this particular occasion). If they had acquired their HIV recently and were highly infectious, it would be much higher.

      Conversely, if you were to get involved with someone who knew their positive status, had been on anti-retrovirals for a long time, had a confirmed low viral load, and with whom you were consequently careful (you avoided high risk activities, and always used condoms), the actual risk of you acquiring HIV in any given sex act might be 1 in 10,000 or even 1 in 100,000, lower than in the above random stranger scenario.

      If you live in a low prevalence part of the country, only have sex with people from lower risk groups or of confirmed negative status, and always use condoms perfectly, the first scenario probably sounds extreme. But it is a scenario that some people find themselves in, which is why HIV is still a problem.

      Does that make sense?

      • Cynthia says:

        Thanks for the explanation.

        I see your point that a high-risk encounter with a stranger is much less safe than a low-risk encounter with someone you know and trust (to tell you their viral load is low, and to take medications as prescribed). But that’s not a one to one comparison like I thought Peter was saying on Twitter.

        If we assume people don’t lie about viral load or status, we’re only dealing with meeting strangers who don’t know their status, which is about 168,000 people in the U.S. Out of 316 million people, I have a 1 out of 1880 chance of meeting someone who is HIV+ and doesn’t know it. So, unless I’m meeting and sleeping with literally thousands of people, isn’t that still safer than exposure to one person of known status and engaging in the same activities?

        I mean, if we average the transmission rates for all stages* and multiply that by the chances that I’ll even meet someone who is HIV+, that ends up being less that what you linked to in your original post as “negligible” (138 out of 10,000). Unless I misunderstood or miscalculated, and I have no medical background, so I might not understand medical statistics, my chances of picking up a stranger at a bar who is HIV+ and doesn’t know their status and then acquiring HIV from that encounter is 638 out of one billion.

        *”The overall rate of HIV transmission observed in these discordant couples, 0.0012/coital act, is consistent with previous estimates from Rakai [12], Europe, and North America [3, 17].”

  2. Cynthia says:

    That link shortener didn’t work! Let’s try again.

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