HPV vaccines are in use since 2006. HPV vaccine safety has been thoroughly assessed both in large trials and in post-marketing studies. Nevertheless vaccine safety concerns are still a potential barrier to successful implementation of HPV vaccination programmes. So far several vaccine scares have been reported throughout the globe and have been effectively amplified by anti-vaccine activists. Most of the times such events have been carefully investigated and any causal relationship with the vaccine has been ruled out. On the other hand, unexpected events coincidentally occurring after HPV vaccination sometime have not been properly assessed contributing to fuel vaccine hesitancy. HPV vaccine safety data and information have been critically reviewed in order to highlight potential pitfalls and to identify good practices for monitoring and assessing HPV vaccine safety.
Safety of both HPV vaccine products has been assessed during the pre-licensure phase in large clinical trials. Most frequent adverse events (AE) related to HPV vaccines were injection site symptoms and general symptoms like fatigue, headache, and myalgia, all transient and without sequelae. Serious AE have been rare (<0.1%) and no more frequent than in placebo group. Autoimmune and neurological conditions being triggered by HPV vaccination have been investigated but no consistent evidence for a causal association has been found. Nevertheless several rumours on serious AEs following HPV vaccination are reported since vaccination programmes started, including alleged fatal outcomes. Long-term follow up of clinical trials and observational studies using pharmacovigilance databases have shown no difference in death rates between vaccinees and the general population. More recently two neurological conditions (Complex Regional Pain Syndrome – CRPS; and Postural Orthostatic Tachycardia Syndrome -POTS) have been allegedly linked to HPV vaccination in Japan and Denmark. The Pharmacovigilance Risk Assessment Committee at the European Medicine Agency has concluded that “the review found no evidence that the overall rates of these syndromes in vaccinated girls were different from expected rates in these age groups”, acknowledging that no causal relationship exists between such conditions and HPV vaccination.
HPV safety monitoring represents a paramount element of the vaccination programme. So far alleged serious AEs following vaccination have been a serious threat for the programme when such events have been not properly investigated. Enhanced surveillance and prompt response systems must be put in place in addition to existing routine passive pharmacovigilance systems.