Adverse Events and Quadrivalent Human Papillomavirus Recombinant Vaccine—Reply

In Reply: Although we are in agreement with Drs Debold and Hurwitz that no single study can stand alone as proof of a vaccine's safety, we want to make several clarifying comments regarding our analyses. The calculation of PRRs or other measures of disproportionality such as the empirical Bayesian geometric mean are standard techniques for the analysis of data from pharmacovigilance systems such as VAERS, in which denominator data are not available for calculation of rates.¹ The proportional distribution of specific adverse events is compared between different vaccines. Doses of vaccine administered or distributed are not used; only data internal to the VAERS database are used. After disproportionality analysis, the number of verified GBS reports following qHPV did not meet criteria to warrant further investigation. However, because GBS has been hypothesized to be associated with multiple vaccines in the past, it is one of the outcomes being assessed in the qHPV active surveillance Vaccine Safety Datalink² protocol, in which the vaccine exposure and adverse outcome are linked on an individual level.