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ABSTRACTThe safety of 9-valent HPV vaccine (9vHPV) has been established with regard to common and uncommon adverse events. However, investigation of rare and severe adverse events requires extended study periods to capture rare outcomes. This observational cohort study investigated the occurrence of three rare and serious adverse events following 9-valent human papillomavirus (9vHPV) vaccination compared to other vaccinations, in US individuals 9–26 years old, using electronic health record data from the Vaccine Safety Datalink (VSD). We searched for occurrences of Guillain-Barré syndrome (GBS), chronic inflammatory demyelinating polyneuropathy (CIDP), and stroke following 9vHPV vaccination from October 4, 2015, through January 2, 2021. We compared the risks of GBS, CIDP, and stroke following 9vHPV vaccination to risks of those outcomes following comparator vaccines commonly given to this age group (Td, Tdap, MenACWY, hepatitis A, and varicella vaccines) from January 1, 2007, through January 2, 2021. We observed 1.2 cases of stroke, 0.3 cases of GBS, and 0.1 cases of CIDP per 100,000 doses of 9vHPV vaccine. After observing more than 1.8 million doses of 9vHPV, we identified no statistically significant increase in risks associated with 9vHPV vaccination for any of these adverse events, either combined or stratified by age (9–17 years of age vs. 18–26 years of age) and sex (males vs. females). Our findings provide additional evidence supporting 9vHPV vaccine safety, over longer time frames and for more serious and rare adverse events.

Few studies have assessed adolescent human papillomavirus (HPV) vaccine attitudes and whether they are associated with vaccination uptake. This study characterized HPV vaccine attitudes among male and female adolescents, identified factors associated with attitude changes, and examined associations between attitudes and vaccination receipt. Surveys were administered to adolescents aged 15–16 years who had not completed the HPV vaccine series. A modified version of the Carolina HPV Immunization Attitudes and Beliefs Scale (CHIAS) was employed to assess barriers, harms, ineffectiveness, and uncertainties scores. Surveys were available from 108 participants; 63% were male and 33% had initiated the HPV vaccine series at baseline. CHIAS scores significantly decreased (i.e., became more favorable) between baseline and follow-up for barriers (p = 0.01) and uncertainties (p < 0.01). At least one sociodemographic/clinical factor was associated with changes in each score. Attitude changes were not associated with receipt of HPV vaccine, although adolescents with higher baseline harms scores were significantly less likely to receive an HPV vaccine dose (OR = 0.67). Adolescents’ HPV vaccine attitudes slightly improved over a one-year period during which an intervention was implemented. More research is needed to learn how parent and adolescent HPV vaccine attitudes form, and how best to address concerns about vaccine harms.