New global modelling shows that without rapid action, poorer countries will fall further behind, even as cervical cancer becomes preventable. At the same time, combined vaccination and screening strategies could close the gap and save millions of lives.
Study: Substantial increases in cervical cancer inequalities worldwide without enhanced human papillomavirus vaccination and screening efforts: a global modelling study. Image credit: Antonio Marca/Shutterstock.com
Global inequalities in cervical cancer are projected to widen dramatically unless enhanced vaccination and screening efforts are implemented, according to a new modeling study published in The Lancet.
Unequal vaccination and screening drive global disparities in cervical cancer
Cervical cancer, the fourth leading form of female cancer, is caused by the human papillomavirus (HPV). It results in more than 600,000 new cases annually worldwide, disproportionately affecting low- and middle-income countries (LMICs).
Age-standardized rates show a threefold higher incidence of cervical cancer in LMICs compared to HICs, with sixfold higher cervical cancer deaths. This high level of inequality is driven by large disparities in both access to cervical cancer screening and HPV vaccination, with screening playing a major role. For instance, only 10 % of women in these countries are screened, versus 84 % in HICs.
Only 23 % of girls in LMICs were vaccinated in 2023, versus 57 % in HICs. Vaccination for girls was introduced only in 2018 in LMICs, but in 2012 in HICs. Boys are vaccinated in most HICs but only 1 % of LMICs. These disparities are driven by multiple factors, including past relatively high vaccine costs, resource constraints, competing health budget demands, limited vaccine supply, and disruptions caused by the COVID-19 pandemic.
These constraints have begun to ease in recent years. Vaccines are now cheaper, supply has improved, and there is increasing evidence of single-dose efficacy. As a result, many more LMICs have introduced HPV vaccination.
Cost-effective tools for cervical cancer elimination
The HPV vaccine and enhanced vaccination programs are extremely cost-effective in preventing cervical cancer. Previous research by the same authors showed that 48–64 doses of the HPV vaccine were needed to prevent one cervical cancer, with one dose administered to females before the age of 20 years. In comparison, more than 10,000 second doses were needed to prevent one case in an HIC-based universal vaccination program. Despite this, HPV vaccine uptake remains very low in most LMICs.
Strategies to eliminate cervical cancer
To counter existing disparities, the World Health Organization (WHO) set cervical cancer elimination as its global strategy in 2020. This is defined as an age-standardized cervical cancer incidence of <4 cases per 100,000 women-years. The WHO's elimination strategy aims to vaccinate 90 % of girls, screen 70 % of women, and treat 90 % of detected lesions.
Examining different strategies for impact on cervical cancer inequalities
The current study sought to examine the impact of various vaccination strategies on the age-standardized cervical cancer incidence. The researchers used the HPV-ADVISE model to predict outcomes across 67 LMICs and 42 high-income countries (HICs) with different enhanced prevention strategies.
In 2022, the age-standardized incidence of cervical cancer in LMICs was threefold that of HICs. This would increase to 12-fold by 2105, according to model predictions.
Switching to the nine-valent vaccine
Under the status quo, cervical cancer incidence in LMICs is projected to decrease by only 23 % by 2105, while HICs would reach elimination by 2048. This would increase inequalities from threefold to 12-fold over the period. Switching all LMICs to the nine-valent vaccine without increasing coverage or screening is projected to have only a minimal impact on incidence and inequalities.
Achieving 90 % vaccination in girls
Increasing vaccination coverage among girls in LMICs to 90 % is a major step towards elimination. With this measure, LMIC-HIC inequality would decrease from 2022 rates to about twofold overall. Cervical cancer would be eliminated in all areas except sub-Saharan Africa, though at different time points; 45 years earlier in HICs than in LMICs.
At 80 % coverage, substantial reductions would still occur, but this level alone would not be sufficient to achieve elimination or equality between LMICs and HICs.
However, the benefits of increased vaccination coverage are delayed, with population-level effects taking approximately 20–40 years to become evident. Thus, during this transition period, inequalities in cervical cancer incidence would rise sevenfold by 2065 before subsiding, due to the delayed rollout of vaccination and lower coverage in LMICs compared to HICs.
Universal vaccination and multi-cohort vaccination
If LMICs adopted a universal and multi-age cohort vaccination routine, elimination status would be achieved in a shorter period, by 2080, 30 years behind HICs. Incidence rates would initially rise in LMICs until around 2055, temporarily increasing the inequality. However, vaccination-only strategies are not expected to substantially reduce cervical cancer incidence in the short term, as they do not address existing infections in older, unvaccinated populations.
Achieving all WHO elimination goals
Either reaching WHO targets or implementing high-coverage universal routine and multi-age cohort vaccination could independently achieve elimination in most LMIC regions and HICs. However, WHO targets offer faster reductions in cervical cancer incidence and inequalities by combining vaccination with screening and treatment. Still, full equality across all LMIC regions would require additional measures.
Overall, meeting WHO targets could accelerate elimination while averting about six million additional cancer cases in the LMICs included in the model.
Combining WHO targets with universal and multi-cohort vaccination
To achieve global equality in cervical cancer incidence, the model suggests that LMICs need to adopt the WHO elimination targets in addition to introducing universal vaccination and multi-age cohort vaccination. This would eliminate cervical cancer worldwide by 2070, with the shortest gap of 20 years between HICs and LMICs, and could avert up to 37 million cervical cancer cases over 100 years compared with the status quo.
Further analyses confirmed these findings.
Study limitations
The study did not include countries in North Africa or the Middle East, which account for about 10 % and 5 % of the global LMIC and HIC population, respectively. Certain very similar vaccination strategies were not separately examined.
Inequalities will widen without urgent global intervention
These findings suggest that without rapidly expanding HPV vaccination and cervical cancer screening programs, global inequalities in cervical cancer incidence will rapidly increase despite this condition being largely preventable. A combination of strategies promises the fastest and most equitable progress towards a cervical cancer-free world.
Future studies should examine the best ways to implement these programs given the wide differences in political and cultural contexts across countries.
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