Real-Life Safety Profile of the 9-Valent HPV Vaccine Based on Data from the Puglia Region of Southern Italy

Abstract

Human Papillomavirus (HPV) is responsible for epithelial lesions and cancers in both males and females. The latest licensed HPV vaccine is Gardasil-9®, a 9-valent HPV vaccine which is effective not only against the high-risk HPV types, but also against the ones responsible for non-cancerous lesions. This report describes adverse events following Gardasil-9® administration reported in Puglia, southern Italy, from January 2018 to November 2021. This is a retrospective observational study. Data about the adverse events following immunization (AEFIs) with Gardasil-9® were collected from the Italian Drug Authority database. AEFIs were classified as serious or non-serious accordingly to World Health Organization guidelines, and serious ones underwent causality assessment. During the study period, 266,647 doses of 9vHPVv were administered in Puglia and 22 AEFIs were reported, with a reporting rate (RR) of 8.25 per 100,000 doses. The most reported symptoms were neurological ones (7/22). A total of 5 (22.7%) AEFIs were classified as serious, and 2 of these led to the patient’s hospitalization. In one case, permanent impairment occurred. Following causality assessment, only 2 out of 5 serious AEFIs were deemed to be consistently associated with the vaccination (RR: 0.750 per 100,000 doses). The data gathered in our study are similar to the pre-licensure evidence as far as the nature of the AEFIs is concerned. The reporting rate, though, is far lower than the ones described in clinical trials, likely due to the different approach to data collection: in our study, data were gathered via passive surveillance, while pre-marketing studies generally employ active calls for this purpose. Gardasil-9®’s safety profile appears to be favorable, with a low rate of serious adverse events and a risk/benefits ratio pending for the latter.