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Vaccine. 2017 Jun 5;35(25):3303-3308. doi: 10.1016/j.vaccine.2017.04.035. Epub 2017 Apr 23.

Case-control vaccine effectiveness studies: Data collection, analysis and reporting results.

Author information

1
National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, 1600 Clifton Rd, Atlanta, GA, USA. Electronic address: jverani@cdc.gov.
2
International Center for Maternal and Newborn Health, Johns Hopkins Bloomberg School of Public Health, 615 N Wolfe St, Baltimore, MD, USA.
3
Rollins School of Public Health Emory University, 1518 Clifton Rd, Atlanta, GA, USA.
4
Department of Immunizations, Vaccines and Biologicals, World Health Organization, 20 Avenue Appia, 1211 Geneva, Switzerland.
5
Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases, 1 Modderfontein Rd, Sandringham, Johannesburg, South Africa.
6
National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, 1600 Clifton Rd, Atlanta, GA, USA.
7
National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, 1600 Clifton Rd, Atlanta, GA, USA; International Vaccine Access Center, Johns Hopkins Bloomberg School of Public Health, 615 N Wolfe St, Baltimore, MD, USA.
8
Respiratory and Meningeal Pathogens Unit, University of Witwatersrand, Richard Ward, 1 Jan Smuts Ave, Braamfontein, Johannesburg, South Africa.
9
Monitoring & Evaluation, Policy & Performance, GAVI Alliance, Chemin des Mines 2, 1202 Geneva, Switzerland.
10
Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases, 1 Modderfontein Rd, Sandringham, Johannesburg, South Africa; Respiratory and Meningeal Pathogens Unit, University of Witwatersrand, Richard Ward, 1 Jan Smuts Ave, Braamfontein, Johannesburg, South Africa.
11
Murdoch Children's Research Institute, Royal Children's Hospital, 50 Flemington Rd, Parkville VIC 3052, Australia; Department of Infectious Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, Keppel St, London WC1E 7HT, UK.
12
International Vaccine Access Center, Johns Hopkins Bloomberg School of Public Health, 615 N Wolfe St, Baltimore, MD, USA.
13
Department of Infectious Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, Keppel St, London WC1E 7HT, UK.
14
Department of Infectious Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, Keppel St, London WC1E 7HT, UK; KEMRI-Wellcome Trust Research Programme, PO Box 230-80108, Kilifi, Kenya.
15
MRC Tropical Epidemiology Group, London School of Tropical Medicine and Hygiene, London, UK.
16
Centre of Intervention Science in Maternal and Child Health and Centre for International Health, University of Bergen, PO Box 7800, Bergen, Norway; Department of International Public Health, Norwegian Institute of Public Health, PO Box 4404, Nydalen, Oslo, Norway.
17
PATH, 2201 Westlake Avenue, Seattle, WA, USA.
18
Aga Khan University, Stadium Rd, Karachi, Pakistan.

Abstract

The case-control methodology is frequently used to evaluate vaccine effectiveness post-licensure. The results of such studies provide important insight into the level of protection afforded by vaccines in a 'real world' context, and are commonly used to guide vaccine policy decisions. However, the potential for bias and confounding are important limitations to this method, and the results of a poorly conducted or incorrectly interpreted case-control study can mislead policies. In 2012, a group of experts met to review recent experience with case-control studies evaluating vaccine effectiveness; we summarize the recommendations of that group regarding best practices for data collection, analysis, and presentation of the results of case-control vaccine effectiveness studies. Vaccination status is the primary exposure of interest, but can be challenging to assess accurately and with minimal bias. Investigators should understand factors associated with vaccination as well as the availability of documented vaccination status in the study context; case-control studies may not be a valid method for evaluating vaccine effectiveness in settings where many children lack a documented immunization history. To avoid bias, it is essential to use the same methods and effort gathering vaccination data from cases and controls. Variables that may confound the association between illness and vaccination are also important to capture as completely as possible, and where relevant, adjust for in the analysis according to the analytic plan. In presenting results from case-control vaccine effectiveness studies, investigators should describe enrollment among eligible cases and controls as well as the proportion with no documented vaccine history. Emphasis should be placed on confidence intervals, rather than point estimates, of vaccine effectiveness. Case-control studies are a useful approach for evaluating vaccine effectiveness; however careful attention must be paid to the collection, analysis and presentation of the data in order to best inform evidence-based vaccine policies.

KEYWORDS:

Case-control studies; Evaluation studies; Vaccines

PMID:
28442230
DOI:
10.1016/j.vaccine.2017.04.035
[Indexed for MEDLINE]
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