Purpose: To assess the potential impact of a human papillomavirus (HPVs) 16/18 vaccination program on oncogenic HPVs prevalence in Italy.
Method: The potential effects of HPV 16/18 vaccine on cervical cancer incidence will depend on how vaccination lowers oncogenic HPV prevalence throughout the population. We developed a dynamic deterministic and non-linear model for heterosexual transmission of HPV infections to describe direct and indirect protection effects of vaccination. The model distinguishes 3 different types of HPV: high-risk 16/18, high-risk non 16/18, and low-risk, and was parametrized using demographic characteristics of the Italian population and published literature on HPV. The model was calibrated to match observed type-specific HPV prevalence. Vaccine efficacy assumptions: 75.6% effective in preventing HPV 16/18 infection, and 11% effective in preventing infection by high-risk HPV types not covered by the vaccine.
Result: At 30% vaccine coverage, vaccinating 12-year-old girls will result in a reduction of HPV 16/18 prevalence and in an increase of high-risk HPV non 16/18 prevalence. Twenty years after the start of the vaccination program high-risk HPV (16/18 and non 16/18) prevalence will decrease for women <35 yrs and will increase for women >35 yrs. After sixty years the prevalence decreases for all age groups except for women aged 40-49 years (see table).
| Age | Equilibrium | After 20 yrs | After 60 yrs |
| years | % | % (variation) | % (variation) |
| 15-19 | 25.3 | 12.0 (-53%) | 9.8 (-61%) |
| 20-24 | 30.6 | 22.5 (-27%) | 17.9 (-42%) |
| 25-29 | 19.2 | 16.0 (-17%) | 12.6 (-35%) |
| 30-34 | 12.0 | 11.6 (-3%) | 9.1 (-24%) |
| 35-39 | 7.5 | 9.6 (+27%) | 6.7 (-11%) |
| 40-44 | 4.9 | 7.7 (+56%) | 5.3 (+8%) |
| 45-49 | 3.3 | 5.0 (+53%) | 3.5 (+6%) |
| 50-54 | 1.9 | 2.7 (+40%) | 1.8 (-3%) |
| 55-59 | 1.6 | 2.2 (+35%) | 1.5 (-6%) |
| 60-64 | 1.7 | 1.8 (+6%) | 1.3 (-24%) |
Conclusion: At 30% coverage, HPV 16/18 vaccination of preadolescent women will lower HPV 16/18 prevalence also among non-vaccinated women. However, the decrease in HPV 16/18 prevalence is accompanied by an increase in high-risk HPV non 16/18 prevalence in the next decades. Overall oncogenic HPV prevalence can increase or decrease depending on age group.
See more of: The 34th Annual Meeting of the Society for Medical Decision Making