Fear versus fear: understanding vaccination rates

All opinions are my own and do not necessarily reflect those of Novo Nordisk.

h/t to @edyong209 for the heads up on the study.

If it seems like plagues from bygone years are coming back, well, you’re right!  Due to growing objections within the United States to vaccination efforts, we are seeing a number of infectious diseases arising that even ten years ago we might have said were eradicated in the US.   The problem may seem larger than it is simply because we get so much more news so much more quickly and easily than we used to.  However, so far there have been 159 cases of measles, which is the highest yearly count since the mid-90s.  And there are still 3.5 months to go in 2013.  Texas has been in the news quite a bit recently for clusters of measles and whooping cough–both diseases with good vaccines that prevent infection when used correctly.

There are a number of reasons why parents choose not to vaccinate their children and one of these seems to be a lack of familiarity with these preventable diseases.  Once almost everyone got the measles and kids got really sick; some died.  Now, the idea of infectious diseases might seem quaint, distant and nonthreatening to parents with no frame of reference.  And of course, once a child gets a disease it’s too late.  A particularly scary report suggests even some younger doctors feel that infectious diseases aren’t such a big deal.

So you might think that this recent study, and others like it showing that the Human Papilloma Virus (HPV) vaccine is clearly reducing HPV infections throughout the body should be promoted even more strongly by public health officials.  Why?  Because HPV is known to cause cancer.  And if there’s anything that evokes the immediacy of fear in the area of health issues, it’s cancer.  That may not be the correct path however, and I’ll get to that in a minute, but first I just want to talk about the research.

The research study was a double-blinded clinical trial in which  7,466 women were inoculated at random with either an HPV vaccine or a control vaccine to hepatitis A.  At the end of the trial, the women were checked for evidence of oral HPV infections.  The vaccine had an estimated vaccine efficacy of about 93%, meaning it reduced infection rates about 14-15 fold.  This study is the first to demonstrate that HPV vaccinations can prevent oral HPV infections in addition to those at the cervix and other locations, as has been shown previously in other research.

That HPV infection is linked causally to the development of some cancers has been shown repeatedly.  Oral HPV infections contribute to the majority of oropharyngeal cancers. When these vaccines were developed, this was the basic argument:  that giving this vaccine to women would result in a decrease in HPV infections and subsequently a decrease in various cancers.  However, as has happened with many vaccines such as the Measles-Mumps-Rubella (MMR) shot, the scientific rationale became overshadowed by a number of other, unanticipated societal factors.

With the HPV vaccine, as Beth Skwarecki (@BethSkw) astutely pointed out on PLOS Blogs, maybe the key issue that wasn’t given enough attention in planning the vaccine rollout is that they way you get HPV is by having sex, and the age at which you should ideally give a person a vaccine is when they are 11 to 12 years old.  Or, to think about it another way, just when girls are starting to begin the maturation process into young women and parents have to face the reality that there is a good chance their child will be having sex sometime in the next 5-10 years.

And that’s scary.  Scarier than the possibility that your child might get cancer 20, 30 years down the road because he or she did not get vaccinated for HPV.  Beth also helpfully links to writing by David Ropeik about how fear can trump common sense with respect to things like, for example, vaccines.

It’s already known that people are lousy about understanding probability, and when you add an element of fear to this misunderstanding, one can see how vaccination campaigns even for something as straightforward as HPV face an uphill battle.

I mean, cancer!  If you can’t get people behind a preventative measure for cancer, what can you do?

And that is the question.  It’s not enough to just say that vaccinations should be mandated.  Sure government could do that, but the consequences could be quite large in terms of anger and pushback.  Would it have helped if in the beginning Merck had not pressed so strongly for every girl to be vaccinated?  Maybe, as some analyses after the fact suggest Merck involvement increased suspicion that all this was just some Pharma boondoggle.  That’s a post-hoc justification though, which I tend to distrust.

Ultimately it seems the answer will have to come from some combination of using subtler methods for incentivizing parents and better understanding of what people are afraid of.  Because right now it seems like even the fear of cancer isn’t enough.

Hanging with the herd, for the immunity of it all

All opinions are my own and do not necessarily reflect those of Novo Nordisk.

When I hear about events such as the recent outbreak of measles among a small group in Texas, I am reminded of how complex, complicated and difficult public health efforts can be. In the US, for example, there are conflicting imperatives:  the rights of people to practice their beliefs versus the right of the community to be protected against preventable health threats.  This particular situation involved members of a church congregation, many of whom had not gotten vaccinated for measles due to worries about a link between autism and the Measles-Mumps-Rubella (MMR) vaccine.  While no scientific evidence has been found to support any such link, many had chosen not to be vaccinated “just in case.”

One day I hope to write about the link between the phenomenon of science denial and personal identity (one perspective can be seen here), but for now I just want to point out how this event and a recent publication by the Centers for Disease Control (CDC) on rotavirus vaccines demonstrate nicely the concept of herd immunity (article behind paywall, but writeup here).  There are different usage patterns for the term, so I’ll say up front I am using “herd immunity” to describe not just the proportion of individuals within a population who are immunized to a given pathogen but also the indirect effects for non-immunized individuals.  The term was first used in a publication in 1923, by Topley and Wilson, in the context of how to describe the host side of their studies in bacterial infection among mice.  The concept later gained mathematical underpinnings, including formulas describing how the different ratios of vaccinated to nonvaccinated individuals defines the degree of herd immunity depending upon how infectious a disease agent is. Continue reading