328. An Unmasking Phenomenon in a Vaccine Safety Study in Adolescents and Young Adults
Session: Poster Abstract Session: Challenges in Vaccinology and Vaccine Exploration
Friday, October 21, 2011
Room: Poster Hall B1
Background:  In observational vaccine safety studies in children, diagnosis codes of chronic conditions assigned on the day of vaccination (day 0) are often excluded from analysis of safety signals since they usually represent pre-existing conditions.  The appropriateness of this approach (excluding day 0 events) has not been critically evaluated in adolescents and young adults, for whom physician visits are not as regular as for younger children.  We draw on our recent experience in a post licensure safety study of the quadrivalent human papillomavirus vaccine (HPV-4) in females to examine this day 0 phenomenon in adolescents and young adults.

 Methods:  Subjects included all 117,402 girls and young women who received HPV-4 from August 2006 to March 2008 in Kaiser Permanente Southern California.  We identified potential incident diabetes cases using ICD9 code 250.xx associated with inpatient and emergency room visits during the 60 days following each HPV-4 dose, excluding those with ICD9 code 250.xx prior to their first HPV-4 dose.  The electronic medical records of the remaining cases were reviewed to determine the date diagnostic labs were ordered and the date the diagnosis of diabetes was applied.

Results:  Of the 33 potential incident diabetes cases identified using automated data, 18 were excluded due to miscoded diagnosis or diabetes diagnoses found in the medical record prior to vaccination.  Fifteen cases of diabetes diagnosed after the date of vaccination were identified.  In nine (60%) of these cases, fasting blood glucose ordered on the day of vaccination was later found to be abnormal, resulting in further work up and application of the diagnosis of diabetes in the following days.  One of the 15 cases occurred during gestation and another case had elevated fasting blood glucose and glucosuria prior to the first dose of HPV-4 but was not diagnosed until after the vaccination.

Conclusion:  These results suggest that among adolescents and young adults, the workup and subsequent diagnosis of pre-existing conditions may result from a visit at which a vaccination is administered.  This “unmasking” phenomenon is not entirely eliminated by exclusion of “Day 0” events and therefore chart abstraction should be considered in the evaluation of potential safety signals.


Subject Category: I. Adult and Pediatric Vaccines

Bradley Ackerson, MD, Harpreet Takhar, MPH, Lina S. Sy, MPH, Jeff Slezak, MS, Chun Chao, PhD, Craig Cheetham, PharmD and Steve Jacobsen, MD, PhD, Research and Evaluation, Kaiser Permanente Southern California, Pasadena, CA


B. Ackerson, None

H. Takhar, None

L. S. Sy, None

J. Slezak, None

C. Chao, Pfizer: Grant Investigator, Research grant
Amgen: Grant Investigator, Research grant
Merck: Grant Investigator, Research grant

C. Cheetham, None

S. Jacobsen, None

Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.