Effect of HPV vaccination and cervical cancer screening in England by ethnicity: a modelling study

Abstract

Background: Health equality is increasingly being considered alongside overall health gain when assessing public health interventions. However, the trade-off between the direct effects of vaccination and herd immunity could lead to unintuitive consequences for the distribution of disease burden within a population. We used a transmission dynamic model of human papillomavirus (HPV) to investigate the effect of ethnic disparities in vaccine and cervical screening uptake on inequality in disease incidence in England.

Methods: We developed an individual-based model of HPV transmission and disease, parameterising it with the latest data for sexual behaviour (from National Survey of Sexual Attitudes and Lifestyles [Natsal-3]) and vaccine and screening uptake by ethnicity (from Public Health England [PHE]) and fitting it to data for HPV prevalence (from ARTISTIC, PHE, Natsal-3) and HPV-related disease incidence (from National Cancer Registry [ONS]). The outcome of interest was the age-adjusted incidence of HPV-related cancer (both cervical and non-cervical) in all women in England in view of differences and changes in vaccination and screening uptake by ethnicity in England, over time. We also studied three potential public health interventions aimed at reducing inequality in HPV-related disease incidence: increasing uptake in black and Asian females to match that in whites for vaccination; cervical screening in women who turn 25 in 2018 or later; and cervical screening in all ages.

Findings: In the pre-vaccination era, before 2008, women from ethnic minorities in England reported a disproportionate share of cervical disease. Our model suggests that Asian women were 1·7 times (95% credibility interval [CI] 1·1-2·7) more likely to be diagnosed with cervical cancer than white women (22·8 vs 13·4 cases per 100 000 women). Because HPV vaccination uptake is lower in ethnic minorities, we predict an initial widening of this gap, with cervical cancer incidence in Asian women up to 2·5 times higher (95% CI 1·3-4·8) than in white women 20 years after vaccine introduction (corresponding to an additional 10·8 [95% CI 10·1-11·5] cases every year). In time, we predict that herd immunity benefits will diffuse from the larger white sub-population and the disparity will narrow. Increased cervical screening uptake in vaccinated women from ethnic minorities would lead to rapid improvement in equality with parity in incidence after 20 years of HPV vaccination.

Interpretation: Our study suggests that the introduction of HPV vaccination in England will initially widen a pre-existing disparity in the incidence of HPV-related cancer by ethnicity, partly due to herd immunity disproportionately benefiting subgroups with high vaccination rates. Although in time this induced disparity will narrow, increasing cervical screening uptake in girls from ethnic minorities should be encouraged to eliminate the inequality in cervical cancer incidence in the medium term. We recommend that dynamic effects should be considered when estimating the effect of public health programmes on equality.

Funding: Cancer Research UK.

Figure 1

Uptake of cervical screening and HPV vaccination by ethnicity Cervical screening attendance by ethnicity as estimated by Natsal-3 and Public Health England (A). We termed “recent” screening to be within the past 5 or past 10 years for those younger or older than 50 years, respectively, thereby including women who were overdue a routine appointment. Uptake of HPV vaccination for the routine cohort and two catch-up cohorts, by ethnic group based on data obtained from the clinical practice research datalink (B) and primary care trusts (C). Bar height shows proportion of women receiving at least one dose; light blue shows the subset fully vaccinated.

Figure 2

Model-predicted incidence of cancer by ethnicity, over time (A) Annual incidence of cervical cancer per 100 000 white, black, and Asian women. (B) Annual incidence of HPV-attributable non-cervical cancer per 100 000 members of the white, black, and Asian populations. Bar height shows the mean model output for 100 simulations, the error bars the 95% credibility interval.

Figure 3

Rate ratios of model-predicted cervical cancer incidence over time comparing (A) Asian with white women and (B) black with white women Figure shows the effect of HPV vaccination introduction as our base case scenario, together with three potential interventions for addressing the resultant increase in inequality. We estimated the effect of increasing ethnic minority uptake of HPV vaccination, cervical screening in the routine vaccination cohort, and cervical screening of all ages to match the levels observed in the white sub-population. Interventions were made in 2018 (10 years after the introduction of the HPV vaccine).

Figure 4

Absolute difference in model-predicted cervical cancer incidence per 100 000 women over time comparing (A) Asian with white women and (B) black with white women