Bias with respect to socioeconomic status: A closer look at zip code matching in a pneumococcal vaccine effectiveness study.
In 2010, 13-valent pneumococcal conjugate vaccine (PCV13) was introduced in the US for prevention of invasive pneumococcal disease in children. Individual-level socioeconomic status (SES) is a potential confounder of the estimated effectiveness of PCV13 and is often controlled for in observational studies using zip code as a proxy. We assessed the utility of zip code matching for control of SES in a post-licensure evaluation of the effectiveness of PCV13 (calculated as [1-matched odds ratio]*100). We used a directed acyclic graph to identify subsets of confounders and collected SES variables from birth certificates, geo-coding, a parent interview, and follow-up with medical providers. Cases tended to be more affluent than eligible controls (for example, 48.3% of cases had private insurance vs. 44.6% of eligible controls), but less affluent than enrolled controls (52.9% of whom had private insurance). Control of confounding subsets, however, did not result in a meaningful change in estimated vaccine effectiveness (original estimate: 85.1%, 95% CI 74.8-91.9%; adjusted estimate: 82.5%, 95% CI 65.6-91.1%). In the context of a post-licensure vaccine effectiveness study, zip code appears to be an adequate, though not perfect, proxy for individual SES.
National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, 1600 Clifton Road, MS C-25, Atlanta, GA 30329, USA; Department of Epidemiology, University of North Carolina at Chapel Hill, 135 Dauer Drive, Chapel Hill, NC 27516, USA.
Ruth
R
Link-Gelles
Department of Epidemiology, University of North Carolina at Chapel Hill, 135 Dauer Drive, Chapel Hill, NC 27516, USA.
Daniel
D
Westreich
Department of Epidemiology, University of North Carolina at Chapel Hill, 135 Dauer Drive, Chapel Hill, NC 27516, USA.
Allison E
AE
Aiello
Department of Epidemiology, University of North Carolina at Chapel Hill, 135 Dauer Drive, Chapel Hill, NC 27516, USA.
Nong
N
Shang
Department of Epidemiology, University of North Carolina at Chapel Hill, 135 Dauer Drive, Chapel Hill, NC 27516, USA.
David J
DJ
Weber
Minnesota Department of Health, P.O. Box 64975, St. Paul, MN 55164, USA.
Corinne
C
Holtzman
Institute for Public Health, University of New Mexico, Emerging Infections Program, 1601 Randolph SE, Suite 1005, Albuquerque, NM 87106, USA.
Karen
K
Scherzinger
California Emerging Infections Program, 360 22nd Street, Suite 750, Oakland, CA 94612, USA.
Arthur
A
Reingold
Department of Preventive Medicine, Vanderbilt University School of Medicine, 1500 21st Avenue South, Suite 2600, Nashville, TN 37212, USA.
William
W
Schaffner
Department of International Health, Johns Hopkins Bloomberg School of Public Health, 201 W. Preston Street, Baltimore, MD 21201, USA.
Lee H
LH
Harrison
New York City Department of Health and Mental Hygiene, 125 Worth St, New York, NY 10013, USA.
Jennifer B
JB
Rosen
Connecticut Department of Public Health, 410 Capitol Avenue, Hartford, CT 06134, USA.
Susan
S
Petit
Division of Infectious Diseases, Emory University School of Medicine, Atlanta, GA, USA; Infection Disease Section, Medical Specialty Care Service Line, Atlanta VA Medical Center, 1670 Clairmont Road, Station 152, Decatur, GA 30033, USA.
Monica
M
Farley
Oregon Public Health Division and Oregon Emerging Infections Program, 800 NE Oregon Street, Suite 772, Portland, OR 97232, USA.
Ann
A
Thomas
Bureau of Epidemiology, Utah Department of Health, 288 N 1460 W, Salt Lake City, UT 84116, USA.
Jeffrey
J
Eason
County of Los Angeles Department of Public Health, 313 N Figueroa St, Los Angeles, CA 90012, USA.
Christine
C
Wigen
Colorado Emerging Infections Program, 4300 Cherry Creek Drive South, Denver, CO 80246, USA.
Meghan
M
Barnes
County of Los Angeles Department of Public Health, 313 N Figueroa St, Los Angeles, CA 90012, USA.
Ola
O
Thomas
New York State Department of Health, Corning Tower, Room 651, Empire State Plaza, Albany, NY 12237, USA.
Shelley
S
Zansky
National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, 1600 Clifton Road, MS C-25, Atlanta, GA 30329, USA.
Bernard
B
Beall
National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, 1600 Clifton Road, MS C-25, Atlanta, GA 30329, USA.
Cynthia G
CG
Whitney
National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, 1600 Clifton Road, MS C-25, Atlanta, GA 30329, USA.
Matthew R
MR
Moore
Matched case-control; PCV13; Pneumococcal vaccine; Pneumococcus; Socioeconomic status; Vaccine effectiveness
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