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a Divisions of Infectious Diseases
c General Pediatrics, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania
b Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
| ABSTRACT |
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METHODS. The public-use files of the National Immunization Survey were used to estimate annual MMR coverage from 1995 to 2004. The primary outcome was selective measles-mumps-rubella nonreceipt, that is, those children who received all childhood immunizations except MMR. Media coverage was measured by using LexisNexis, a comprehensive database of national and local news media. Factors associated with MMR nonreceipt were identified by using a logistic regression model.
RESULTS. Selective MMR nonreceipt, occurring in as few as 0.77% of children in the 1995 cohort, rose to 2.1% in the 2000 National Immunization Survey. Children included in the 2000 National Immunization Survey were born when the putative link between MMR and autism surfaced in the medical literature but before any significant media attention occurred. Selective nonreceipt was more prevalent in private practices and unrelated to family characteristics. MMR nonreceipt returned to baseline before sustained media coverage of the MMR-autism story began.
CONCLUSIONS. There was a significant increase in selective MMR nonreceipt that was temporally associated with the publication of the original scientific literature, suggesting a link between MMR and autism, which preceded media coverage of the MMR-autism controversy. This finding suggests a limited influence of mainstream media on MMR immunization in the United States.
Key Words: media impact vaccines
Abbreviations: MMR—measles-mumps-rubella vaccine NIS—National Immunization Survey OR—odds ratio CI—confidence interval
The last decade has seen a steady growth in the production and availability of new vaccines to the pediatric market. During the past 2 years alone, 4 new vaccines were introduced into the routine pediatric immunization schedule in the United States, and 3 existing vaccines were given new indications.1 This expansion in vaccine recommendations has been met by increasing concern for vaccine safety raised by individuals who question the potential for vaccine adverse effects despite a lack of reliable data to support these claims.2 In the face of this growing skepticism, the challenge for our public health community is to better understand how physician and public perception of vaccines and vaccine-preventable diseases affects vaccine uptake.
Perhaps one of the best opportunities to examine the influence of public perception on vaccine uptake is to focus on the putative link between the measles-mumps-rubella (MMR) vaccine and autism first put forth by Wakefield et al in February 1998.3 Although this study was significantly flawed and later discredited,4 it was widely publicized in the British press. Consequently, national rates of MMR coverage in Britain fell from 92% to 73%, with rates in parts of London as low as 50%.5 This decrease in coverage resulted in measles outbreaks6 and the first measles death in the United Kingdom in more than a decade.5 Although there was a dramatic impact on MMR receipt in Britain, the impact of the Wakefield et al3 study and its subsequent media coverage have never been studied nationally in the United States, despite concern within the public health community.7 The potential impact is not a trivial question. In May 2005, a measles outbreak affected 34 individuals in Indiana, 32 of whom were unvaccinated. The primary reason for vaccine declination was concern for adverse events, specifically those related to media reports of the potential link between MMR and autism.8
The current study aimed to provide for the first time population-level estimates of MMR receipt in the United States after the publication of the article by Wakefield et al3 and its subsequent media coverage. Our specific goals were to determine the temporal impact of the publication of this article3 on MMR receipt in the country, whether media exposure of the controversy was associated with changes in MMR receipt, and which, if any, regional-level, system-level, and child-level characteristics were associated with changes in MMR receipt.
| METHODS |
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The outcome variables obtained from the public use files of the NIS between 1995 and 2004 were related to the receipt of MMR vaccine. One outcome of interest was overall MMR nonreceipt, which indicated all of the children who had not received the MMR vaccine. However, a potential concern in measuring MMR nonreceipt alone is the effect of other factors, notably, poverty and access to medical care, that have been associated with poor immunization rates in the past.10 To better understand intentional MMR nonreceipt, we also identified those children who received all of the childhood immunizations except MMR. Children were defined as having selective MMR nonreceipt if they were up to date for 3 hepatitis B, 3 polio, 4 diphtheria-tetanus-acellular pertussis, and 3 Haemophilus influenzae type b vaccines but not MMR.
The NIS also allowed us to collect other covariates, including gender, age group at time of survey (19–23, 24–29, or 30–35 months), race (Hispanic, non-Hispanic white, non-Hispanic black, or other), census region (Northeast, Midwest, West, or South), family income ($0 to $30 000, $30 001 to $50 000, more than $50 000, or unknown), level of maternal education (<12 years, no college, some college, or college degree), maternal marital status (currently married or not), firstborn status of the child, and medical provider type (all public, all private, other, or mixed). Public providers included public health clinics and community health centers. Private providers included private clinics, health maintenance organizations, and group practices. Other providers included all other types of providers, such as hospitals, military facilities, and unknown responses. Mixed providers included >1 type of provider.
The source of data for media exposure was the LexisNexis Academic Universe (Lexis Nexis, Dayton, OH), a database of national and local television, national and local newsprint, and national and local radio. This database has been widely used in the communications literature and in previous studies of media coverage of vaccines11,12 and other medical topics, including breast cancer,13 diabetes,14 and medication safety.15,16 LexisNexis includes data from 295 newspapers in the United States, including the top 25 circulating papers and 90 of the top 100. It also captures all of the Associated Press newswire releases, all of the major television networks (ABC, CBS, Fox, NBC, and CNN), and National Public Radio broadcasts. All of the stories captured by the search terms "MMR" and "autism," or "measles" and "autism," or "Wakefield" and "MMR," or "Wakefield" and "autism," in story headline, lead paragraph, and terms were recorded. These search terms were culled from a longer list of search strategies after empiric testing with the LexisNexis database. Because the oldest children in the 1995 NIS were born in 1992, we searched LexisNexis from 1992 to 2004. Articles or stories not specifically about vaccines were excluded. All of the stories had their specific day and time, as well as region of the country recorded.
Data were described using frequencies for all of the categorical variables. There were no continuous variables reported. The frequencies of overall and selective MMR nonreceipt were calculated for each year in the study period. The NIS weights for children with adequate provider data were used to provide nationally representative estimates for each year.17 Because the NIS includes children born over a 30-month period, media exposure for each survey year was calculated as the total number of stories to which the cohort was potentially exposed during the first year of life. Although media coverage could not be linked to families at the child level, these data were graphically superimposed on the cross-sectional immunization data to permit a temporal comparison.
In addition to the graphical representation of the data, we also performed repeated cross-sectional analyses using logistic regression models to assess risk factors for overall and selective MMR nonreceipt. All of the analyses were adjusted by using the NIS sample weights for children with adequate provider data. Predictor variables, including child and family demographic characteristics, health care provider characteristics, and year of survey (for secular trends), were chosen for the model based on their significance in univariate testing. Additional interaction was explored independently of the results of univariate analysis based on a priori hypotheses. These potential interactions included the differential impact of the type of health care provider by year on immunization rates, family characteristics by year on MMR nonreceipt, and health care provider by region of country. Results from these analyses are presented as odds ratios (ORs) with associated 95% confidence intervals (CIs).
All of the statistical analyses were performed by using Stata 9.0 (Stata Corp, College Station, TX). This study was granted exempt status by the Children's Hospital of Philadelphia Committees for Protection of Human Subjects.
| RESULTS |
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10% of 19- to 35-month-old children did not receive the MMR vaccine. This decreased to 8% in 1998 then increased again to 10% in 2000 before falling to 7% in 2003 and 2004. Selective MMR nonreceipt increased from <1% from 1995–1999 to 2.2% in 2000, then returned to baseline over the next 2 years.
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| DISCUSSION |
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1 in 50 children missed the opportunity for MMR immunization, and the rates were as high as 1 in 40 among children in private practices (data not shown). Significant media coverage of the MMR-autism controversy did not begin until nearly 2 years after this measurable increase in nonreceipt. To our surprise, selective MMR nonreceipt had already returned to baseline by the time this increased media coverage occurred. In the absence of widely reported newsprint, television, or radio reports, the likely explanation for the brief increase in MMR nonreceipt is that parents learned about the MMR-autism controversy from other sources. Although the NIS does not ask parents how they obtain information about vaccines, our data provide insight into the decision-making process surrounding childhood vaccination. Essentially, the decision to immunize a child is influenced by 1 of 3 factors: the parent's willingness to immunize the child, the health care provider's attitude and input toward guiding this decision-making, and the availability of the vaccine. The only MMR shortage in the United States during the study period began in the winter of 2001, well after the observed increase in selective MMR nonreceipt, and did not affect receipt of the first MMR dose.18 Therefore, only 2 plausible explanations for our observations remain: either families or physicians (or some combination of the two) became more reluctant to receive or provide the MMR vaccine.
One potential source of information for parents may have been the Internet. Nearly 70% of Americans access the Internet each day,19 and 13% of adult Internet users state that they have specifically searched for information about vaccines online.20 At the same time, the number of antivaccination Web sites has increased over the past decade.21,22 However, in 1998, only 35% of households had access to the Internet,19 and there were fewer antivaccination Web sites. Had the Internet played a large role in MMR nonreceipt, we might have expected higher family income to be associated with MMR nonreceipt, but we did not see this relationship.
Another potential explanation for our findings is that some medical providers, made aware of the article by Wakefield et al3 through discussion in medical journals, may have become hesitant to administer the MMR vaccine. Several studies have reported that physicians are the most influential source of immunization information for parents,23–25 including those who believe that vaccines are unsafe26 and those who request exemptions.27 Even if physicians were not the primary source of information about the MMR-autism controversy, they still would have been influential in the decision-making process. Bates et al28 in 1994 found that, among children in an inner-city pediatric clinic, provider attitudes and behaviors were more important predictors of immunization status than parental beliefs. Another study of children in a private-practice cohort found that provider- and practice-associated characteristics were significantly associated with up-to-date immunization status, whereas family and child level characteristics were not.29
That physicians may play an important role in MMR delivery is further supported by the finding that neither selective nor overall MMR receipt changed significantly in the face of increased media coverage of the MMR-autism controversy that occurred after 1999, a time when families were more likely to be confronting their physicians with vaccine safety concerns during well-child visits. Why did MMR receipt not change significantly during this period? To some extent, daycare-entry and school-entry requirements may have preserved MMR coverage in this country. In addition, the greatest intensity of media coverage was associated with an Institute of Medicine report that refuted any link between the MMR vaccine and autism. This report, and the epidemiologic studies cited in it, may have reassured physicians and parents. Also, the MMR vaccine had been in routine pediatric use for many years with a demonstrated favorable risk/benefit and safety profile. Indeed, previous data has shown that physicians perceive older vaccines to be more important than newer vaccines.30 Finally, in comparison with other vaccine-preventable diseases, physicians' perception of measles severity was likely tied to recent memory after a resurgence of measles in the United States in the late 1980s and early 1990s, which resulted in 11 000 hospitalizations and 120 deaths.31
There are limitations that may impact the interpretation of our findings. One concern is that our data on media coverage may be incomplete. Although recent work has supported the validity of media database searches,32 we only relied on 1 source, the publicly available LexisNexis Academic Universe, for our primary analysis. To test the sensitivity of our analysis to the choice of media database, we separately replicated our search methods with a more comprehensive version of LexisNexis, which is only available through private license. That search did increase the amplitude of the curve depicted in Fig 2 but did not change its overall shape. No additional periods of media activity were identified between 1998 and 2000 when there was minimal media coverage in our original analysis. Similarly, restriction of the media analysis to the top 5 circulating newspapers, the 5 major news networks, and the Associated Press newswire reduced the total number of stories but did not affect the temporal distribution of media coverage. The lack of media attention between 1998 and 2000 is not surprising; its relationship to immunization practice parallels the history of media coverage of other pediatric medication-related controversies. For instance, Reye syndrome, a severe form of liver disease associated with aspirin use during viral illness, was first described in the medical literature as isolated case reports that received little media coverage. The media did not widely report this story until larger epidemiologic studies were performed over the next several years. By the time this media coverage peaked, parents had already begun to switch from aspirin to acetaminophen with a resultant decrease in disease incidence.33
Other potential limitations include insufficient data on the content of news stories, response bias in the immunization survey, and generalizability to current vaccine practice. We chose not to qualify the content of news stories, because previous studies have shown that even the mention of a controversy in the media may impact public awareness regardless of specific content.34,35 In addition, many reports presented both sides of the controversy equally, and in Britain this "balanced journalism" resulted in the public perception that there was equal scientific evidence supporting both sides, when this was not the case.36 With respect to response bias, because we only included provider-verified data, it is possible that parents with vaccine safety concerns would have been unintentionally excluded because they may not have agreed to participate in an immunization survey or to attend the practices included in the survey. However, the exclusion of such parents in this study would bias our results toward the null. Finally, the generalizability of these data to more recent vaccines and their uptake in the community is perhaps a more important concern. It is possible that limited physician experience with newer vaccines may result in more significant and sustained reductions in use during periods of media scrutiny. The effects of recent safety concerns on the uptake of the newly licensed meningococcal and rotavirus vaccines will need to be followed closely to determine whether the media may have a more dramatic impact on uptake than we observed with the MMR vaccine.
Despite these limitations, these data still offer important lessons for our public health community as it confronts new threats to public acceptance of emerging vaccines. Although causal relationships are difficult to discern from these data, our findings suggest that physicians may have been an important buffer against the potential negative impact of media coverage of immunization controversies. As the media increasingly reflect the concerns of a skeptical public, public health officials must value the provider community as its best opportunity to confront these challenges. If providers do indeed become more cautious during periods of controversy, then the focus for public health officials should be on ensuring that providers are given timely advisories and access to credible recommendations. The lesson for the public health community may thus be that the willingness to immunize a child is a story played out in the examination room during the private conversation between a doctor and a family. Keeping the doctor frequently updated with the most credible information and with strategies for discussing vaccine safety with parents may be the most efficient way to guarantee successful immunization practices in the face of increasing amounts of often unreliable and misleading information.
| ACKNOWLEDGMENTS |
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We thank Daniel Romer, PhD, and Robert Hornik, PhD, from the Annenberg School of Communication, for their help in measuring and interpreting media coverage of medical news and Paul Offit, MD, from the Children's Hospital of Philadelphia, for his review of this article. None of these individuals received financial compensation for their contributions.
| FOOTNOTES |
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Address correspondence to Michael J. Smith, MD, Division of Pediatric Infectious Diseases, University of Louisville School of Medicine, 571 S Floyd St, Suite 321, Louisville, KY 40202. E-mail: mjsmit22{at}louisville.edu
The authors have indicated they have no financial relationships relevant to this article to disclose.
| What's Known on This Subject In 1998, researchers suggested a link between MMR and autism. Although significantly flawed, this article was widely reported in the British media, with a subsequent decrease in MMR immunization.
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| What This Study Adds This study is the first to measure the population-level impact of the MMR controversy in the United States and the first to quantify coverage of the MMR autism debate in the American media.
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