PEDIATRICS Vol. 117 No. 2 February 2006, pp. 387-390 (doi:10.1542/peds.2004-2687)
Vaccine Adverse Event Reporting System Reporting Source: A Possible Source of Bias in Longitudinal Studies
HealthPartners Research Foundation, Minneapolis, Minnesota
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ABSTRACT |
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 TOP ABSTRACT METHODSRESULTSDISCUSSIONREFERENCES |
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OBJECTIVE. The US Vaccine Adverse Event Reporting System (VAERS) is a passive reporting system to which anyone can report an event. Publicity related to potential adverse events may change reporting patterns. The objective of this paper is to show how litigation-related reports have influenced the trends in possible adverse event reports to VAERS.
METHODS. The VAERS public-use data files were downloaded in July 2004 and translated into identical SAS data sets for analysis. Cases that were related to litigation were identified using a word search algorithm. All cases for the most frequently reported symptoms in litigation (overdose, neuropathy, autism, "mental retardation," arthralgia, and "speech disorder") were reviewed.
RESULTS. In recent years, most case reports to VAERS that were related to overdose, neuropathy, and thimerosal were related to litigation. Many cases that were related to autism and mental retardation were as well.
CONCLUSIONS. This review shows a previously undisclosed rise in the number of reports to the VAERS related to pending litigation for vaccine injury. The implications of this for understanding longitudinal reporting patterns are discussed.
Key Words: VAERS • adverse event reporting systems
Abbreviations: VAERS—Vaccine Adverse Event Reporting System • MMR—measles-mumps-rubella • VICP—Vaccine Injury Compensation Program • COSTART—Coding Symbols for a Thesaurus of Adverse Reaction Terms
THE VACCINE ADVERSE Event Reporting System (VAERS) is an important passive surveillance tool.1–7 The system is designed to operate as an early warning system, primarily for generating hypotheses.5,6 VAERS receives spontaneous reports from manufacturers, medical professionals, parents, and others with knowledge of an event that might be associated with a vaccine. Because it does not include a denominator, testing for causality is not possible with VAERS. There have been, however, longitudinal studies of changes in reporting of events after the change from vaccines that contained whole-cell pertussis to vaccines that contained acellular pertussis.1
It is widely known that reports to the VAERS are influenced by other published reports suggesting an association between a vaccine and an adverse event. A recent study of autism reports to VAERS from 1990 to 20018 found that 
75% of autism reports in VAERS were received at approximately the time of the publication of the British case series linking gastrointestinal symptoms, autism, and measles-mumps-rubella (MMR) vaccine by Wakefield (London, United Kingdom),9 and two thirds were received after the American Academy of Pediatrics/Public Health Service recommendation to remove the mercury-containing preservative thimerosal from vaccines.10
Although VAERS does not support assessment of causality, data from VAERS has been used, primarily by Geier and Geier, to document the increasing rate of autism reports with increasing dose of thimerosal and increasing use of MMR.11–14 These and other, similar studies are used by litigants who seek compensation under the Vaccine Injury Compensation Program (VICP) as evidence that as the number of immunizations has increased and the presumed load of thimerosal has increased, the rate of autism has increased.
Given that there is substantial potential for manipulation of the VAERS data, the purpose of this article is to document for pediatricians the volume and the type of attorney-generated reports to VAERS. It is appropriate for attorneys to make reports to VAERS. The VAERS web site says the following about reporting: anyone can report to VAERS. The majority of VAERS reports are sent in by vaccine manufacturers (42%) and health care providers (30%). The remaining reports are obtained from state immunization programs (12%), vaccine recipients (or their parent/guardians; 7%), and other sources (9%). Vaccine recipients or their parents or guardians are encouraged to seek the help of their health care professional in filling out the VAERS form (www.vaers.org/vaers.htm#2).
However, when VAERS may be manipulated inappropriately to influence litigation and public policy, it is important to understand this distortion. Specifically, because VAERS data have been used to study the effect of vaccines on changes in disease rates, it is important to understand the effect that various reporting sources have on rate calculations over time.
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METHODS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONREFERENCES |
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The data for this study come from the 1990 through 2003 public-use data files (www.vaers.org/data.htm#1). These are comma-delimited files, which then have been converted to Microsoft Excel 2000 files and then imported into SAS data files for analysis. The intermediate Excel step was required to avoid truncating text fields during the import process.
The "symptom text" field is used to identify reports that are related to litigation. Each word in the symptom text field is translated to a single variable. All words in this field were output and reviewed for words that indicated legal intent. Those that contained the words "lawyer," "legal," or "attorney" or the substring "litigat" then were output as cases that were related to lawsuits. Records in which "legal" was accompanied by "guardian" were excluded (6 cases) because they did not relate to litigation. After this step, the data were reduced back to a single record per report to avoid duplicate counting.
VAERS staff use the reporter's symptom description to create an array of diagnoses using the Coding Symbols for a Thesaurus of Adverse Reaction Terms (COSTART) developed and maintained by the Food and Drug Administration's Center for Drug Evaluation and Research. For each record, we saved all coded COSTART symptoms and all coded vaccines, as well as the vaccine receipt date and the reporting date. The vaccine receipt date is missing in 8% of VAERS records but in 27% of the VAERS reports that were related to litigation. In this report, therefore, we focus only on reporting date. All symptoms from a single report were considered without regard to listed order.
Outcomes were identified from the symptom array of up to 20 symptoms. Several reported outcomes were examined to illustrate the importance of litigation-based reports. For each outcome, the number of reported cases in each year and the number from litigation are compared. From the litigation-related VAERS records, the most common symptoms from the symptom array were selected. The records from nonlitigation records with these symptoms then were selected. For analysis, we focus on the following symptoms: overdose, neuropathy, autism, "mental retardation," arthralgia, and "speech disorder." Because of coding differences in young children, we combined the COSTART term "thinking abnormality" with autism.
One additional analysis was done using the symptom text field. To find cases that were related to the preservative thimerosal, we searched the symptom text field for the strings "THIM," "MERCU," and "THIO." Those that were related to allergic reaction or hypersensitivity reaction were eliminated from the data set (46 cases). This was done to remove cases with the well-documented allergic reaction to thimerosal and focus on those that were most similar to the litigation-related cases.
At the end of the file preparation, the reports for each symptom listed above were available, both among cases that were related to litigation and those that were not related to litigation. This was also true for the term "thimerosal."
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RESULTS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONREFERENCES |
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Table 1 shows the number of records that were related to litigation. The results indicate that these reports are sharply increasing with a total of 477 in the data reviewed. The data are separated into those that were related to Lyme vaccine, which was marketed from early 1999 until March 2002, and other vaccine reports to show that the increase in reports does not represent an effect that is attributable solely to the Lymerix vaccine. The decline in 2003 reports is probably because of processing delays in creating the public-use files. The number of litigation-related reports is small before 2000 and peaks in this data set in 2002.
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Analysis of Table 2 shows that overdose, neuropathy, and nonallergy thimerosal cases from litigation are more than one half of the litigation-related reported events in 2002 and 2003. Overdose, as used here, refers to the COSTART term. For autism (including thinking abnormality), nearly one third of reports in 2002 were related to litigation, and for mental retardation, it was nearly one half of reports. For nonallergy thimerosal, overdose, and neuropathy, the vast majority of the cases reported were related to litigation.
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DISCUSSION |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONREFERENCES |
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The results of this article show a clear increase in VAERS reports related to litigation. Longitudinal analysis of adverse event reports that fail to take reporting source into account will not portray accurately the trend that they imply in the data. Pediatricians who review these analyses or are asked by concerned parents to comment on data from a well-respected source, such as VAERS, need to be aware of and conversant in how the data are derived. This article, hopefully, fills some of that gap.
The findings raise an important question about possible misuse of VAERS in the litigation process. When a study is being used to influence important public health decisions, it is important that reviewers and editors fully understand how the data were constructed and their source. Until now, no one has described the magnitude of litigation-related reporting and how these reports might potentially change the results of studies using VAERS data. Longitudinal studies using VAERS data should explicitly take into account changes in reporting sources like the one described in this article.
It is impossible to determine the effect of these reports on existing analyses because the existing literature does not describe carefully inclusion and exclusion criteria. For the conditions reviewed here, it is apparent that a large enough percentage of reports are being made related to litigation that failure to exclude these will seriously skew trends. This is important for vaccines that contain thimerosal, and specifically for the MMR vaccine because of the controversy surrounding its relationship to autism. It therefore is incumbent on the authors who use VAERS data to provide detailed methods sections that describe their inclusion and exclusion criteria. To that end, we are making our SAS code available to interested parties. It is not sufficient simply to reference extraction of the VAERS data set.
Our results are probably conservative. Discussions with VAERS staff at the Centers for Disease Control and Prevention about reports that are generated from the VICP indicate that we may have missed some litigation-related cases because our code identified only a subset of these cases (John Iskander, personal communication, August 6, 2004). We tested code to identify VICP cases but were unable to find a way to identify them. Underascertainment of cases that are related to litigation, however, only strengthens our point. The influence of the litigation process on longitudinal analyses is a serious matter and emphasizes the importance of interpreting VAERS data cautiously.
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ACKNOWLEDGMENTS |
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We appreciate the helpful comments from Centers for Disease Control and Prevention staff on the use and interpretation of the public-use VAERS data sets.
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FOOTNOTES |
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Accepted May 5, 2005.
Address correspondence to Michael J. Goodman, PhD, HealthPartners Research Foundation, 8100 34th Ave South, Minneapolis, MN 55440. E-mail: michael.j.goodman{at}healthpartners.com
The authors have indicated they have no financial relationships relevant to this article to disclose.
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PEDIATRICS (ISSN 1098-4275). ©2006 by the American Academy of Pediatrics
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