Apr 17 2008

Media Coverage Influence on MMR Vaccination Rates

A new study published in the current issue of Pediatrics looks at the association between mainstream media coverage of the claim that there is a possible correlation between the mumps measles rubella vaccine (MMR) and autism and the rate at which American parents refused the MMR vaccine for their children. The results were a bit surprising.

Smith et. al. used the LexisNexis database to track media reports of Wakefield’s initial study showing a possible connection between MMR and vaccines (the study was later discredited, and to date there is no evidence to support such a connection). They compared this to data reporting the incidence of parents refusing just the MMR component of the routine childhood vaccine schedule (so-called selective MMR nonreceipt). Their hypothesis was that media coverage would correlate with an increased incidence of selectively refusing the MMR. But that is not what they found.

What they did find is that in the 1995 cohort selective MMR nonreceipt was 0.77%. This increased to 2.1% in 2000, shortly after Wakefield published his study, but then returned back down to baseline over the next two years, before the spike in media coverage of the MMR-autism controversy. Therefore an increase in MMR refusal correlated with the scientific publication of a possible MMR-autism connection, but not with mainstream media coverage of the story. What’s going on?

The authors cover several possible explanations for this data, but I am most compelled by one in particular, which was the explanation that first occurred to me. The LexisNexis media database includes traditional media outlets, but not the internet. In my experience concerns over vaccines and autism is largely an internet phenomenon. Antivaccination groups picked up on Wakefield’s study very quickly and soon anyone searching the internet for information on vaccines would come across dire warnings of the possible risks of MMR.

What this study may be telling us more than anything is that people are now going to the internet for this type of information more than traditional media. Also – searching online for information is an active process. People doing this typically have a specific question, or are facing an important decision and are trying to inform themselves. Mainstream media, on the other hand, is more passive – consumers receive whatever news is chosen for them.

Another factor discussed by the authors is the possibility that pediatricians were primarily responsible for the decline in MMR compliance. Pediatricians were likely aware of the Wakefield study and the controversy even prior to lay media coverage, and this could have introduced a bit of doubt in the safety of MMR. Perhaps this doubt was not enough to stop recommending and giving the vaccine, but if parents expressed concerns about the safety of MMR some pediatricians may have hedged their support given the uncertainty introduced by Wakefield’s study.

This study also confirms what was previously observed, that the overall effect of the vaccine-autism controversy in the United States one vaccine compliance has been relatively small. Although there are indications that that more recently the effect may be growing. For example there has been a larger number of parents who are taking the religious exemption in order to refuse vaccines for their children. Also, while the overall MMR numbers are good, there have been pockets of high refusal rates within certain communities. this has resulted in outgreaks. For example, in May 2005 there was a measles outbreak in Indiana affecting 34 people, 32 of whom were unvaccinated.

In the UK the effect of the MMR scare was much more profound. MMR vaccination rates plummeted to only 83%, well below the 95% rate needed for herd immunity (where enough people are vaccinated to prevent an infection from spreading through a population).  At the same time the number of measles cases increased dramatically, with 971 cases in 2007.

It is critically important that accurate an unbiased information about vaccines be given to the public. While the internet is a boon to the free flow of information, it also provides a venue for ideologically driven misinformation – and its effects are likely surpassing that of the mainstream media, especially for certain kinds of information, like health information. This highlights the importance of scientists and the medical community taking the time to provide accurate and authoritative information on the internet.

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