Adverse Events and Quadrivalent Human Papillomavirus Recombinant Vaccine

To the Editor: Dr Slade and colleagues¹ evaluated reports submitted to the Vaccine Adverse Event Reporting System (VAERS) for quadrivalent human papillomavirus recombinant vaccine (qHPV). Federal officials have cited this study as evidence that qHPV “is a safe and effective vaccine.”² However, we consider that conclusion to be unwarranted because the study draws inferences from data likely to be systematically biased, and because the design of the study cannot disprove causal associations at the individual level.