Impacts of human papillomavirus vaccination for different populations: A modeling study

Abstract

International variations in the prevalence of HPV infection derive from differences in sexual behaviors, which are also a key factor of the basic reproductive number (R₀ ) of HPV infection in different populations. R₀ affects the strength of herd protection and hence the impact of a vaccination program. Similar vaccination programs may therefore generate different levels of impact depending upon the population's pre-vaccination HPV prevalence. We used IARC's transmission model to estimate (i) the overall effectiveness of vaccination versus no vaccination in women aged 15-34 years measured as percent prevalence reduction (%PR) of HPV16 and (ii) the corresponding herd protection in populations with gender-equal or traditional sexual behavior and with different levels of sexual activity, corresponding to pre-vaccination HPV16 prevalence from 1 to 8% as observed worldwide. Between populations with different levels of gender-equal sexual activity, the highest difference in %PR under girls-only vaccination is observed at 40% coverage (91%PR vs. 48%PR for 1% and 8% pre-vaccination prevalence, respectively). HPV16 elimination is obtained with 55 and 97% coverage, respectively. To achieve desirable levels of HPV16 prevalence after vaccination, different levels of coverage are required in populations with different levels of pre-vaccination HPV16 prevalence, for example, in populations with gender-equal sexual behavior a decrease to 1/1000 HPV16 from pre-vaccination prevalence of 1 and 8% would require coverages of 37 and 96%, respectively. In traditional populations, corresponding coverages would need to be 28 and 93%, respectively. In conclusion, pre-vaccination HPV prevalence strongly influences herd immunity and helps predict the overall effectiveness of HPV vaccination.

Keywords: HPV prevalence; HPV vaccination; coverage threshold; herd effect.

Figure 1

Assumed mean number of new sexual partners per year, by class of sexual activity for population with gender‐equal sexual behavior (a)11 and traditional sexual behavior (b).14

Figure 2

HPV16 prevalence (%) in sexually active women aged 15–35 years (Data are from IARC Prevalence Surveys, 1990–2016).5 The size of the dot is proportional to the number of women recruited in each survey.

Figure 3

(a) Mean annual number of new sexual partners and (b) Basic reproductive number (R ₀) by pre‐vaccination HPV16 prevalence and type of a population's sexual behavior.

Figure 4

(a) Relative reduction in HPV16 prevalence and (b) Achievable post‐vaccination HPV16 prevalence, among women 15–34 years of age after vaccination of 11 year‐old girls in a population with gender‐equal sexual behavior, by coverage and pre‐vaccination prevalence. (c) Relative reduction in HPV16 prevalence and (d) Achievable post‐vaccination HPV16 prevalence, among women 15–34 years of age after vaccination of 11 year‐old girls in a population with traditional sexual behavior, by coverage and pre‐vaccination HPV16 prevalence.