Model-based evaluation of an infant HPV prophylactic vaccination program in Nigeria
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Background
Nigeria introduced single-dose HPV vaccination for girls aged 9–14 in 2023, reaching approximately 60% aggregate coverage by 2025. While an important achievement, this remains short of the 90% coverage called for under the WHO’s 90-70-90 cervical cancer elimination targets, and further scale-up depends on reaching out-of-school girls. In this study we used a model of HPV transmission in Nigeria to quantify the residual cervical cancer burden under continued adolescent delivery, assess how additional screening scale-up and equity assumptions modify it, and identify the effective coverage requirements for an infant HPV vaccination program to be non-inferior to the existing adolescent strategy.
Methods
We used HPVsim, an agent-based microsimulation calibrated to Nigerian sexual behavior, HPV prevalence, and cervical cancer incidence, to project new cervical cancer cases and age-standardized incidence over 2025–2100 under scenarios which vary vaccination delivery mode (status-quo adolescent, WHO 90-70-90 adolescent scale-up, and 60/75/90% infant delivery), screening coverage (opportunistic 15% vs. scaled 70% aggregate), and the degree to which primary school completion correlated with vaccination (odds ratio 1 vs. 5) and with screening (odds ratio 1 vs. 3). Infant delivery scenarios were run at hypothetical effective-vaccine-efficacy-at-exposure values of 50%, 70%, and 95% — scenario inputs bracketing the plausible waning range, not evidence-based estimates of infant vaccine performance (no HPV vaccine trial has enrolled anyone below age 10). Each scenario was run at 50 replicates (10 calibration draws × 5 seeds); reported outcomes are the median across replicates and uncertainty ranges are interquartile (25th–75th percentile).
Results
Continuation of Nigeria’s current adolescent program is projected to avert 1.82 million cervical cancer cases (IQR 1.65–1.90 million; 95% UI 1.39–2.02 million) over 2025–2100 (a 53% reduction relative to no vaccination, IQR 51–55%; 95% UI 46–58%), with age-standardized incidence falling from 19.7 to 7.8 per 100,000 by 2100. However, 82% of the near-term (2025–2075) burden is projected to fall on the pre-2015 birth cohort, i.e. women already beyond the vaccination target age, leaving approximately 945,000 residual cases (IQR 905K–1.00M; 95% UI 835K–1.14M) in this cohort. Scaling up screening to WHO targets was estimated to avert a further ∼387K cases (IQR 331–424K; 95% UI 269–515K), roughly 25% of the residual burden; results were about 6–8% better if the scale-up instead reached all women equitably regardless of education. Under a hypothetical scenario of infant vaccination at 90% coverage and 95% effective vaccine efficacy at exposure (matching adolescent-age performance), outcomes were comparable to full WHO adolescent scale-up (49% vs. 54% reduction in vaccine-targetable cohort cancers), but under a hypothetical 50% effective efficacy at Nigeria’s DTP3-anchored 62% coverage the strategy averted only a fraction of these cancers.
Conclusions
The near-term cervical cancer burden in Nigeria is dominated by cohorts vaccination cannot reach; scaling screening for them is the more consequential lever over the coming three decades and rests on established evidence. Findings on infant HPV delivery are exploratory and hypothesis-generating: they depend on three unverified empirical prerequisites – infant HPV vaccine immunogenicity in the first months of life, durability of protection across the ∼15–25-year interval to peak HPV exposure, and coverage achievable through Nigeria’s routine childhood immunization platform – and should not be read as a basis for any policy recommendation contingent on infant HPV delivery until those prerequisites are established.
