Safety profile assessment of HPV4 and HPV9 vaccines through the passive surveillance system of the Veneto Region (Italy) between 2008 and 2022: A 15-year retrospective observational study

In Veneto Region, HPV vaccine has been actively offered to 12 year-old females since 2008, and to 12 year-old males since 2015. The study aims to analyze the safety profile of HPV4v and HPV9v vaccines and perform a case-by-case review of conditions of interest. Spontaneous reports related to HPV uploaded to the database of the Regional Pharmacovigilance Center between 2008-2022 were included. HPV vaccine doses administered until April 2022 in the Veneto Region were considered to calculate the reporting rate (RR). Potential "safety concerns" examined as conditions of interest were included through Standardized MedDRA or preferred terms searching queries. The level of diagnostic certainty was evaluated as per the Brighton Collaboration case definition criteria. A total of 637 reports and 1316 Adverse Events Following Immunizations (AEFI) were retrieved: 469 for HPV4v (73.6 %) and 168 for HPV9v (26.4 %). Serious reports were 71 (11.1 %): 49 (10.4 %) for HPV4v and 22 (13.1 %) for HPV9v. The RR for serious events between 2008-2022 was 6.9/100,000 administered doses, with no differences by vaccine type. Females and adults showed higher overall RR compared to males and to children and adolescents (p < 0.001), this result was confirmed by stratifying analysis by vaccine type. One case of Guillain Barré syndrome, anaphylactic shock, thrombocytopenia, Henoch Schoenlein purpura and four generalized seizures were reviewed. Vaccinovigilance data from the Veneto Region reaffirm a good safety profile for HPV vaccination and found no vaccine-related unexpected events. Such a detailed analysis may assist healthcare providers to advocate properly for HPV vaccination.