A new global model shows that even if cervical cancer becomes preventable, poor countries will fall further behind without swift action. At the same time, vaccination and screening strategies combined have the potential to close the gap and save millions of lives.
Study: Without increased human papillomavirus vaccination and screening efforts, cervical cancer inequalities will increase significantly around the world: a global modeling study. Image credit: Antonio Marca/Shutterstock.com
Global inequalities in cervical cancer are projected to widen dramatically unless vaccination and screening efforts are stepped up, according to a new modeling study published in . lancet.
Inequitable vaccination and screening drive global disparities in cervical cancer
Cervical cancer, the fourth most common cancer in women, is caused by the human papillomavirus (HPV). This results in more than 600,000 new infections per year worldwide, disproportionately impacting low- and middle-income countries (LMICs).
Age-standardized rates show that LMICs have three times higher cervical cancer incidence and six times higher cervical cancer mortality rates compared to HICs. This high level of inequality This is due to large disparities in access to both cervical cancer screening and HPV vaccination, with screening playing a major role. For example, only 10% of women in these countries have been tested, compared to 84% in HIC.
In 2023, only 23% of girls in LMICs were vaccinated, compared to 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% in LMICs. These disparities are driven by multiple factors, including historically high vaccine costs, resource constraints, competing health budget demands, limited vaccine supplies, and disruptions caused by the COVID-19 pandemic.
These constraints have begun to be relaxed in recent years. Vaccines are now cheaper, supplies are improving, and there is growing evidence of the effectiveness of single doses. As a result, more LMICs have introduced HPV vaccination.
A cost-effective tool to eradicate cervical cancer
HPV vaccines and enhanced vaccination programs are highly cost-effective in preventing cervical cancer. Previous research by the same authors showed that 48 to 64 doses of HPV vaccine are needed to prevent one case of cervical cancer, with one dose given to women under 20 years of age. In comparison, the HIC-based universal vaccination program required more than 10,000 second doses to prevent one case. Nevertheless, HPV vaccine uptake remains very low in most LMICs.
Strategies to eliminate cervical cancer
To combat existing disparities, the World Health Organization (WHO) has set the elimination of cervical cancer as a global strategy for 2020. This is defined as an age-standardized incidence of cervical cancer of less than 4 per 100,000 women. The WHO’s elimination strategy aims to vaccinate 90% of girls, screen 70% of women and treat 90% of detected lesions.
Considering different strategies to impact cervical cancer inequalities
The current study aims to investigate the impact of different vaccination strategies on age-standardized cervical cancer incidence. Researchers used the HPV-ADVISE model to predict outcomes from different enhanced prevention strategies in 67 LMICs and 42 high-income countries (HICs).
In 2022, the age-standardized incidence of cervical cancer in LMICs was three times higher than in HICs. Models predict this will increase 12 times by 2105.
Switching to 9-valent vaccine
Currently, cervical cancer incidence in LMICs is projected to decline by only 23% by 2105, while HIC is expected to reach elimination by 2048. This would lead to a 3- to 12-fold increase in inequality over this period. Switching all LMICs to the 9-valent vaccine without expanding coverage or screening is expected to have minimal impact on incidence and inequality.
Achieved 90% vaccination rate for girls
Increasing vaccination rates to 90% among girls in LMICs is a major step toward elimination. This measure would result in an overall reduction in inequality between LMICs and HICs of approximately double from 2022 rates. Cervical cancer will be eradicated in all regions except sub-Saharan Africa, although at different times. HICs are 45 years earlier than LMICs.
Although 80% coverage would still result in significant reductions, this level alone would not be sufficient to achieve elimination or parity for LMICs and HICs.
However, the benefits of increased vaccination coverage have been delayed, with population-level effects taking approximately 20 to 40 years to become apparent. Therefore, during this transition period, due to slower vaccination rollouts and lower coverage in LMICs compared to HICs, inequalities in cervical cancer incidence are expected to increase sevenfold by 2065 and then subside.
Universal vaccination and multi-cohort vaccination
If LMICs adopted universal multi-age cohort vaccination routines, elimination status would be achieved more quickly, by 2080, 30 years later than HIC. Incidence rates in LMICs will initially increase until around 2055, with a temporary increase in inequality. However, vaccination-only strategies are not expected to significantly reduce cervical cancer incidence in the short term because they do not address existing infections in unvaccinated older adults.
Achieve all WHO elimination targets
Elimination could be achieved independently in most LMIC regions and HICs by meeting WHO targets or implementing high coverage universal routine vaccination and multi-age cohort vaccination. However, WHO’s goal is to reduce cervical cancer incidence and inequalities more quickly by combining vaccination with screening and treatment. Still, additional measures will be needed to achieve full equality in all LMIC regions.
Overall, achieving WHO targets could accelerate elimination while avoiding approximately 6 million additional cancer cases in LMICs included in the model.
Combining WHO targets with universal and multi-cohort vaccination
This model suggests that in addition to the introduction of universal vaccination and multi-age cohort vaccination, LMICs will need to adopt the WHO elimination goals to achieve global equity in cervical cancer incidence. This would reduce the minimum interval between HICs and LMICs to 20 years, eliminate cervical cancer worldwide by 2070, and potentially avoid up to 37 million cases of cervical cancer over 100 years compared to the current situation.
Further analyzes confirmed these findings.
Research limitations
The study did not include countries in North Africa and the Middle East, which account for approximately 10% and 5% of the world’s LMIC and HIC populations, respectively. Certain very similar vaccination strategies have not been considered separately.
Inequality will rise without urgent global intervention
These findings suggest that without rapid expansion of HPV vaccination and cervical cancer screening programs, global inequalities in cervical cancer incidence will rapidly widen, even though the disease is largely preventable. Together, the strategies promise the fastest and most equitable progress towards a world without cervical cancer.
Future research should consider how best to implement these programs, taking into account the vast differences in the political and cultural contexts of each country.
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