Generalisability of vaccine effectiveness estimates: an analysis of cases included in a postlicensure evaluation of 13-valent pneumococcal conjugate vaccine in the USA

• Type of Material: Article
• Authors: Ruth Link-Gelles, Centers for Disease Control and Prevention; Daniel Westreich, University of North Carolina; Allison E. Aiello, University of North Carolina; Nong Shang, Centers for Disease Control and Prevention; David J. Weber, University of North Carolina; Jennifer B. Rosen, New York City Department of Health and Mental Hygiene; Tasneem Motala, County of Los Angeles Department of Public Health; Laurene Mascola, County of Los Angeles Department of Public Health; Jeffery Eason, Utah Department of Health; Karen Scherzinger, University of New Mexico; Corinne Holtzman, Minnesota Department of Health; Arthur L. Reingold, California Emerging Infections Program; Meghan Barnes, Colorado Emerging Infections Program; Susan Petit, Connecticut Department of Public Health; Monica Farley, Emory University; Lee H. Harrison, Johns Hopkins University; Shelley Zansky, New York State Department of Health; Ann Thomas, Oregon Emerging Infections Program; William Schaffner, Vanderbilt University; Lesley McGee, Centers for Disease Control and Prevention; Cynthia Whitney, Emory University; Matthew R. Moore, Centers for Disease Control and Prevention
• Language: English
• Date: 2017-08-01
• Publisher: BMJ PUBLISHING GROUP
• Publication Version: Final Published Version
• Copyright Statement: © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.
• License: Creative Commons Attribution-NonCommercial 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1136/bmjopen-2017-017715
• Title of Journal or Parent Work: BMJ OPEN
• Volume: 7
• Issue: 8
• Start Page: e017715
• End Page: e017715
• Grant/Funding Information: This work was supported by the CDC.
• Keywords: DISPARITIES; Medicine, General & Internal; Life Sciences & Biomedicine; Science & Technology; DISEASE; EXTERNAL VALIDITY; ADEQUACY; General & Internal Medicine; RANDOMIZED CONTROLLED-TRIALS; CLINICAL-TRIALS; PREVENTION; EXPOSURE; INDEX; SOCIOECONOMIC-STATUS
• Research Categories: Health Sciences, Public Health; Biology, Virology

Abstract

Objectives External validity, or generalisability, is the measure of how well results from a study pertain to individuals in the target population. We assessed generalisability, with respect to socioeconomic status, of estimates from a matched case-control study of 13-valent pneumococcal conjugate vaccine effectiveness for the prevention of invasive pneumococcal disease in children in the USA. Design Matched case-control study. Setting Thirteen active surveillance sites for invasive pneumococcal disease in the USA. Participants Cases were identified from active surveillance and controls were age and zip code matched. Outcome measures Socioeconomic status was assessed at the individual level via parent interview (for enrolled individuals only) and birth certificate data (for both enrolled and unenrolled individuals) and at the neighbourhood level by geocoding to the census tract (for both enrolled and unenrolled individuals). Prediction models were used to determine if socioeconomic status was associated with enrolment. Results We enrolled 54.6% of 1211 eligible cases and found a trend toward enrolled cases being more affluent than unenrolled cases. Enrolled cases were slightly more likely to have private insurance at birth (p=0.08) and have mothers with at least some college education (p<0.01). Enrolled cases also tended to come from more affluent census tracts. Despite these differences, our best predictive model for enrolment yielded a concordance statistic of only 0.703, indicating mediocre predictive value. Variables retained in the final model were assessed for effect measure modification, and none were found to be significant modifiers of vaccine effectiveness. Conclusions We conclude that although enrolled cases are somewhat more affluent than unenrolled cases, our estimates are externally valid with respect to socioeconomic status. Our analysis provides evidence that this study design can yield valid estimates and the assessing generalisability of observational data is feasible, even when unenrolled individuals cannot be contacted.