Impact of Vaccinating Adult Women Who Are HPV-Positive or with Confirmed Cervical SIL with the 9-Valent Vaccine—A Systematic Review

Infection with oncogenic human papillomavirus (HPV) remains a leading cause of cervical cancer and other HPV-related diseases. This situation persists despite the availability of effective prophylactic vaccines. While global vaccination programs have significantly reduced the incidence of HPV in adolescents and young adults, many women presenting with HPV infection or squamous intraepithelial lesions (SIL) were not covered by primary prevention. This review was performed with the aim of evaluating the impact of administering the 9-valent HPV vaccine in adult women who are HPV-positive or have histologically confirmed cervical precancerous lesions. Following the PRISMA 2020 guidelines, a search was performed in the MEDLINE, Scopus, and Cochrane Library databases. A total of 653 studies were retrieved, of which 7 studies, including 19,414 women, met the inclusion criteria. According to the literature, vaccination was linked to significant reductions in persistent HPV infection, progression of SIL, and recurrence of high-grade lesions after surgical removal. Complete HPV remission was achieved in up to 72.4% of vaccinated women, compared to 45.7% among unvaccinated controls. Vaccination after conization lowered the recurrence risk of CIN2+ lesions by 87%, with benefits seen regardless of timing. The most significant effect was observed when vaccine administration was performed before the surgical procedure. Furthermore, HPV vaccination notably enhanced viral clearance and decreased the likelihood of repeated surgical interventions. Despite differences in study design and follow-up definitions, the overall evidence supports additional vaccination in HPV-positive adult women as an effective measure to reduce recurrence and promote viral remission. These findings emphasize the need for clear guidelines and wider access to HPV vaccination for adult populations.