To the Editor In their landmark guide, Orenstein et al1 established 4 preconditions for valid field estimation of vaccine effectiveness (VE) using observational designs, including (1) use of a uniform case definition; (2) equal case ascertainment; (3) accurate vaccination-status ascertainment; and (4) comparable virus-exposure risk.1 The equivalent of preconditions 1 and 2 for the test-negative design (TND) is standardization of the testing indication used to identify cases (test-positives) and controls (test-negatives), as also emphasized by others.2,3
Skowronski DM, De Serres G. Application of the Test-Negative Design to General Laboratory Submissions. JAMA Pediatr. Published online December 10, 2018. doi:10.1001/jamapediatrics.2018.4370
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