Public Health Impact of Switching from a 4-Valent to a 9-Valent HPV Vaccination Program in Chile

OBJECTIVES: In Chile, a school-based vaccination program with the human papillomavirus quadrivalent vaccine (4vHPV) was introduced into the National Immunization Program in 2014 for 9-year girls and expanded for 9-year boys in 2018. We aimed to estimate the expected public health impact of a gender-neutral vaccination (GNV) program with a nonavalent HPV-vaccine (9vHPV; HPV6/11/16/18/31/33/45/52/58) compared to the current program with 4vHPV; HPV6/11/16/18).

METHODS: A validated HPV disease transmission dynamic model was calibrated to compare a 9vHPV GNV strategy with 80% VCR for 9- years girls and boys against the current 4vHPV GNV program with 80% VCR. The model assumed two-dose schedule over a 100-year time-horizon, lifelong immunity following vaccination, ongoing cytology screening, and herd immunity. Chile-specific data were used for calibration. The outcomes were incidence reduction and incremental averted cases and deaths of cervical cancer (CC), cervical intraepithelial neoplasia (CIN) 1-3, and non-cervical cancers (vagina/vulva/anus/head and neck/penis).

RESULTS: Compared to the current vaccination program, after 100 years a 9vHPV GNV program is estimated to further reduce the incidence of CC by 21.1%; CIN2/3 by 47.9 2%; CIN1 by 56.2%; male and female anal cancer by 6.0% and 11.3%; penile cancer by 18.6%; and male and female head and neck cancer by 10.6% and 13.7%, respectively. Therefore, 9vHPV will avoid 146,122 additional cases (16,231 female cancers/CIN 1-3 and 1,350 male cancers) and 8,595 deaths related to HPV 31/33/45/52/58-related disease compared to 4vHPV over 100 years.

CONCLUSIONS: Switching to 9vHPV in Chile is projected to provide a substantial public health impact, with faster and greater reduction in the incidence of cervical cancer/CIN 1-3 and non-cervical cancers due to additional protection against HPV 31/33/45/52/58 relative to the current strategy.