Durability of single-dose HPV vaccination in young Kenyan women: randomized controlled trial 3-year results

Cervical cancer burden is high where prophylactic vaccination and screening coverage are low. We demonstrated in a multicenter randomized, double-blind, controlled trial that single-dose human papillomavirus (HPV) vaccination had high vaccine efficacy (VE) against persistent infection at 18 months in Kenyan women. Here, we report findings of this trial through 3 years of follow-up. Overall, 2,275 healthy women aged 15–20 years were recruited and randomly assigned to receive bivalent (n = 760), nonavalent (n = 758) or control (n = 757) vaccine. The primary outcome was incident-persistent vaccine type-specific cervical HPV infection. The primary evaluation was superiority analysis in the modified intention-to-treat (mITT) HPV 16/18 and HPV 16/18/31/33/45/52/58 cohorts. The trial met its prespecified end points of vaccine type-specific persistent HPV infection. A total of 75 incident-persistent infections were detected in the HPV 16/18 mITT cohort: 2 in the bivalent group, 1 in the nonavalent group and 72 in the control group. Nonavalent VE was 98.8% (95% CI 91.3–99.8%, P < 0.0001) and bivalent VE was 97.5% (95% CI 90.0–99.4%, P < 0.0001). Overall, 89 persistent infections were detected in the HPV 16/18/31/33/45/52/58 mITT cohort: 5 in the nonavalent group and 84 in the control group; nonavalent VE was 95.5% (95% CI 89.0–98.2%, P < 0.0001). There were no vaccine-related severe adverse events. Three years after vaccination, single-dose HPV vaccination was highly efficacious, safe and conferred durable protection. ClinicalTrials.gov no. NCT03675256.

One hundred percent of participants received their assigned vaccine and no administration errors were identified.Overall, 19 of 2,275 (0.8%) participants did not contribute follow-up time after enrollment and 5 (0.2%) exited the study during follow-up.Overall, 2,256 of 2,275 (99%) participants contributed a median of 35 months of follow-up time between December 2018 and January 2023.A total of 34% of participants (771 of 2,256) provided a final analysis swab at month 30 and 62% (1,397 of 2,256) at month 36 as participants received cross-over vaccination at their next study visit after regulatory approvals were obtained to allow timely access to the effective intervention.Retention of four or more swabs collected at follow-up for the assessment of primary end points was 96% (2,182 of 2,275) and 91% (2,061 of 2,2,275) for five or more swabs (Extended Data Table 2).Of the end-point swabs, 93% of swabs were cervical and 7% of swabs were self-collected vaginal swabs, which was similar across intention-to-treat (ITT) and mITT cohorts (Extended Data Table 3).

Primary outcomes
Through month 36, a total of 75 incident-persistent infections were detected in the HPV 16/18 mITT cohort: 1 among the nonavalent vaccine group, 2 among participants assigned to the bivalent vaccine group, and 72 among those assigned to the control vaccine group (Table 2a) (thus, no additional infections in the nonavalent group, one additional infection in the bivalent group and 36 additional infections in the control group compared to month 18).Through month 36, the incidence of persistent HPV 16/18 was 0.08 per 100 woman-years in the nonavalent vaccine group and 0.16 per 100 woman-years in the bivalent group, compared to 6.70 per 100 woman-years in the control vaccine control needed to achieve the WHO goal of cervical cancer elimination and to reduce global cervical cancer disparities.
HPV vaccines prevent more than 90% of persistent oncogenic vaccine type-specific HPV infections, the primary cause of cervical cancer 2,3 .HPV vaccination is foundational in the WHO's Global Cervical Cancer Elimination Strategy as a primary prevention of HPV infection 4 .The strategy aims to vaccinate 90% of girls globally.Four HPV vaccines are licensed to be given as 2-3 intramuscular injections over 2-6 months, all targeting high-risk (oncogenic) HPV types that cause 70-90% of cancers.The bivalent vaccines (Cervarix and Cecolin) prevent HPV 16/18 infection, the quadrivalent vaccine (Gardasil) prevents HPV 16/18/6/11, including the low-risk HPV types 6 and 11 to prevent genital warts, and the nonavalent vaccine (Gardasil-9) prevents HPV 16/18/31/33/45/52/58/6/11 infection, including five additional high-risk HPV types.Vaccinating the current global cohort of women aged 9-18 years would prevent HPV-associated precancerous lesions 5 and 11.6 million cases of cervical cancer over their lifetimes 6 ; however, current HPV vaccine coverage remains low.In 2019, only 15% of adolescent girls globally were vaccinated against HPV 7 .
Single-dose HPV vaccination would simplify the logistics and reduce costs of scaling up vaccine programs, lowering barriers to reaching high HPV vaccine coverage.The vaccine virus-like-particle (VLP) structure, which self-assembles to mimic the live virus without the replicating DNA, generates strong immunity with a single dose, analogous to highly immunogenic whole-virus vaccines rather than a subunit vaccine, supporting a biological mechanism for single-dose efficacy rather than the prime-boost multi-dose schedule that optimizes subunit vaccine efficacy (VE) 8 .Single-dose HPV vaccine efficacy is comparable to the licensed two-or three-dose regimen in randomized trials and observational studies [9][10][11][12] .Thus, in April 2022, the WHO recommended one or two doses of HPV vaccines for children, adolescents and young adults aged 9-20 years; however, a desire for data about longer-term durability of single-dose HPV vaccination persists [13][14][15] and national guidelines continue to recommend multi-dose strategies.Also, few low-HDI countries have catch-up vaccination programs for persons 15 years and older, although those programs accelerate the impact of vaccination 5 .
In Kenya, the age-standardized incidence for cervical cancer is 31.3 per 100,000 person-years; annually, an estimated 5,236 new cases are diagnosed and 3,211 deaths attributable to cervical cancer occur 1 .Kenya's two-dose HPV immunization program was launched in October 2019 to reach 10-year-old girls, in the context of vaccine supply constraints.In 2021, vaccine coverage for the first dose was 77% and 31% for the second dose 16 .With WHO guidance recommending vaccination for the multi-age cohort of 9-14 year olds, the easing of vaccine supply constraints, and the need to deliver immunization services to a larger number of adolescents, evaluating the efficacy of single-dose vaccination would provide evidence to policymakers for immunization scale-up, including multi-age cohorts and catch-up vaccination for those who may have missed vaccination during programmatic scale-up.
This study evaluated zero versus single-dose HPV vaccination and employed a superiority design to support efficacious, feasible, and timely evidence for catch-up vaccination 17,18 .As reported previously, at 18 months, bivalent and nonavalent vaccine efficacy was 97.5% for HPV 16/18 and nonavalent VE was 88.9% for HPV 16/18/31/33/45/52/58 10 .We hypothesized that single-dose HPV VE would be durable over 36 months.Here we report the final single-dose HPV VE 3 years after vaccine administration to evaluate the durability of single-dose HPV vaccination for zero versus single-dose HPV vaccination.As planned, all participants have received HPV vaccination and follow-up continues to evaluate the durability of single-dose efficacy.

Participant disposition and characteristics
Between 20 December 2018 and 15 November 2019, 3,090 participants were screened for study eligibility and 2,275 (74%) were enrolled.

Secondary outcomes and efficacy analyses
In the planned secondary sensitivity analysis, including participants with type-specific HPV antibodies detected at enrollment, there were 88 incident-persistent infections in the HPV 16/18 mITT cohort: 1 in the nonavalent vaccine group, 3 among participants assigned to the bivalent group and 84 among those assigned to the control vaccine group (Table 2a).HPV 16/18 incidence was 0.07 per 100 women-years in the nonavalent group, 0.21 per 100 women-years in the bivalent vaccine group and 6.87 per 100 women-years in the control group; nonavalent VE was 99.0% (95% CI 92.5-99.9%,P < 0.0001) and bivalent VE was 96.8% (95% CI 90.0-99.0%,P < 0.0001; Table 2a).In the sensitivity analysis, there were a total of 124 incident-persistent infections in the HPV 16/18/31/33/45/52/58 mITT cohort: 8 among participants assigned to the nonavalent group and 116 among those assigned to the control group; nonavalent VE was 94.8% (95% CI 89.3-97.4%,P < 0.0001; Table 2b).
In the planned secondary extended-sensitivity analysis, excluding participants with HPV DNA detected at month 6, there were a total of 44 incident-persistent infections in the HPV 16/18 mITT cohort: 0 each among participants assigned to the bivalent and nonavalent vaccine groups and 44 among those assigned to the control vaccine group (Table 2a).HPV 16/18 incidence was 0 per 100 women-years in the nonavalent and bivalent vaccine groups and 5.52 per 100 women-years in

Safety
Serious adverse events (SAEs) were experienced by 201 participants, which included 122 participants with pregnancy-related SAEs, 71 with infections or inflammatory conditions (of which 39 were malaria), 7 injuries and 12 mental health illnesses.Overall, the SAE frequency was similar between groups (Table 3).There were five deaths in the study due to unsafe abortion, sepsis, suicide, hepatocellular carcinoma, complications following an emergency cesarean section for fetal distress and one unknown cause with acute symptoms of cough productive of bloody sputum.SAEs were assessed as not related to the study vaccines.Five participants had abnormal cervical cytology at enrollment and were followed until the lesions resolved or the participant received treatment.Social harms were reported by 0.31% of participants (n = 7), including partner physical and verbal abuse and lack of social support from friends and family for trial participation.

Discussion
Three years after vaccine administration, the high efficacy of both single-dose bivalent or nonavalent HPV vaccine was sustained and durable against vaccine-specific oncogenic HPV infection.Protection against type-specific incident-persistent infection was ≥98% for bivalent and nonavalent vaccine protection against HPV 16/18 and >95% for nonavalent vaccine protection against HPV 16/18/31/33/45/52/58, which cause 70% and 90% of cervical cancer cases, respectively.This together with observed high reductions in the absolute cumulative incidence, the potential for public health impact in the context of disparities by HDI in cervical cancer incidence and mortality 1 is substantial.Saliently, there is high certainty of VE of at least 90% against HPV 16/18; the lower confidence interval limit for the bivalent and nonavalent VE.
Taken in context, these data contribute to a suite of studies that provide evidence for single-dose HPV VE.The Costa Rica vaccine trial (CVT) 12 provided the first observational data for bivalent single-dose HPV vaccine effectiveness and recently demonstrated durability over 16 years 19 .The DoRIS study demonstrated that a single-dose nonavalent .Incidence of persistent HPV by randomized vaccine group in the mITT primary, mITT sensitivity cohorts.For the HPV types specified, the mITT primary cohort includes participants who were HPV DNA and antibody negative at enrollment and DNA negative at month 3; the mITT sensitivity cohort includes participants who were HPV DNA negative at enrollment and month 3; and the extended-sensitivity cohort includes participants who were HPV DNA and antibody negative at enrollment, and DNA negative and months 3 and 6.Woman-years of follow-up time is computed from the month 3 swab collection date for the mITT primary and sensitivity cohorts, and from the month 6 swab collection date in the extended-sensitivity cohort.No multiplicity adjustments were performed.a, Incidence of persistent HPV 16/18 and VE.For the extended-sensitivity cohort comparisons, VE is reported as 100 × (1 − crude incidence rate ratio) due to 0 events in the nonavalent and bivalent HPV vaccine arms.Two-sided log-rank P values are computed for each comparison using the log-rank test.b, Incidence of persistent HPV 16/18/31/33/45/52/58 and VE.Two-sided log-rank P values are computed for each comparison using the log-rank test.

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https://doi.org/10.1038/s41591-023-02658-0or bivalent HPV vaccine produced robust immune responses similar to two doses and three doses among 9-14-year-old girls 20 .The IARC-India study reported durability of single-dose quadrivalent HPV vaccine effectiveness over a decade 11 .Thus, consistent evidence on the efficacy and durability of single-dose HPV vaccination supports the WHO guidance for single-dose implementation to increase vaccine coverage.In mathematical modeling analyses of scale-up, implementation of routine single-dose immunization has the potential to avert most cervical cancer cases compared to two doses, with a durability of 20-30 years, in low-HDI settings 21 .Further, single-dose vaccination can increase coverage among girls in the 9-14-year-old group before they age out of vaccine eligibility and provide catch-up vaccination for those who may have missed the immunization due to the COVID-19 pandemic or other reasons.Of the 11.6 million cases of cervical cancer expected globally among girls born between 2005 and 2014, 75% of the burden will be concentrated in 25 countries largely in Africa and Asia, highlighting the need to focus prevention efforts among recently born girls 5 .Overall, the rate of incident persistent HPV infection in this population of African adolescent girls and young women was high; 13.8 per 100 woman-years in the control group, underscoring the need for effective, scalable vaccine programs that can achieve high coverage and reduce this high incidence of HPV infection and ultimately cervical cancer 22,23 .Catch-up vaccination programs for adolescents and young people aged 15-20 years, who do not qualify for current vaccination programs, have the potential to avert oncogenic persistent infections.Through this head-to-head comparison of bivalent and nonavalent HPV vaccines, sustained VE was demonstrated in the context of high HPV prevalence.Single-dose HPV vaccination could increase vaccine access and coverage and offer a cost-effective strategy for cervical cancer prevention.
The vaccines' underlying immunological mechanism of action could explain the observed VE.The vaccines contain monomers that self-assemble into capsomers and VLPs, a highly immunogenic structure mimicking the ordered, repetitive virus epitope structure and allowing for crosslinking of B cell receptors 8 .This induces high levels of virIon-neutralizing serum antibodies and long-lasting plasma cells, supporting effective and durable VE.We did not see evidence of cross-protection with a single dose of the bivalent vaccine and it may be that two doses are required for cross-protection for the closely related HPV 31/33/45.The confidence interval did not include previous estimates of the multi-dose bivalent strategy of 50% cross-protection for HPV 31/33/45 (ref.5).
The study has several strengths, including its randomized, double-blind controlled design, high retention rate, use of cervical HPV DNA as the outcome measure, determination of incident persistent HPV DNA, head-to-head comparison of the licensed bivalent and nonavalent HPV vaccines in protection against persistent infection with oncogenic HPV types, and duration of follow-up.Moreover, the trial successfully enrolled individuals exposed to HPV infection and retained them in all randomized groups, facilitating a rapid evaluation of single-dose efficacy.Compared to the 18-month analysis, the final analysis VE estimates are stable through 36 months, with higher point-estimates

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https://doi.org/10.1038/s41591-023-02658-0and tighter confidence intervals, as additional follow-up time was accrued beyond the 6-12-month buffer period, during which infections that were prevalent at baseline but not detected at follow-up, and may contribute to a lower estimate of VE 13,14 .
We acknowledge that the study has limitations.First, the median duration of follow-up is 35 months and longer-term durability of single-dose VE in a randomized trial would strengthen the evidence as HPV exposure continues through adulthood.Observational data for single-dose HPV vaccination support efficacy over a decade 11 .While participants in the control group have received single-dose HPV vaccination, we are collecting additional data in this cohort to 54 months post-vaccination 24 .The antibody plateau level for single-dose HPV vaccination is reached by 12 months 9 , suggesting that we have observed steady state efficacy.Second, 7% of primary end-point swabs were self-collected and 93% were provider-collected.All swabs would ideally be collected with one modality; however, the correlation between self-collected vaginal and provider-collected cervical swabs is high 25 and there was no difference in the results when self-collected swabs were excluded.For the preplanned subgroup analyses by sexually transmitted infection (STI) status, the subgroups were defined at enrollment and may have changed over time; however, the incidence of persistent non-vaccine HPV types was comparable through the study in the three study groups.Finally, while the GST-ELISA multiplex assay used to exclude participants with HPV antibodies at enrollment demonstrated overall agreement of 89% with the gold standard secreted alkaline phosphatase pseudovirion-based neutralization assay 26 , misclassification of participants as antibody naive would not be different by study group.Further in sensitivity analysis including participants with HPV antibodies at baseline, overall VE was in keeping with the primary findings (Table 2a,b).
Globally cervical cancer is a leading cause of morbidity and mortality among women in mid-life; it is the second most common cancer and the greatest contributor to cancer-related mortality among women in southern and East Africa carrying a high cost to women, their families and communities 1,27 .Focusing on the cohort of girls and adolescent women who are at risk of developing cervical cancer if not vaccinated, global HPV 16/18 vaccination of women born between 2005 and 2014 would avert 8 million (7.8-8.3)cervical cancer cases and HPV 16/18/31/33/45/52/58 vaccination would avert 10.2 million (10.0-10.6)cases, with 70% of cases averted in low-to-middle HDI countries 6 .Cervical cancer is almost entirely preventable through HPV vaccination.Single-dose HPV vaccination could serve to close the gap between the WHO goal of 90% HPV vaccination coverage by 2030 and the 15% of girls globally currently vaccinated 7 , alleviate vaccine supply constraints 27 and provide global policymakers with options to optimally allocate existing HPV vaccine supply.The most recent Cochrane review of the efficacy of single-dose HPV vaccination highlighted that there was moderate evidence on the durability of VE, which we have now provided with robust data over 3 years 13 .Single-dose HPV vaccination could facilitate rapid scale-up of vaccination worldwide.
Over 36 months, single-dose HPV vaccination offered high protection, >95% VE in preventing incident, persistent HPV 16/18/31/33/45/52/58 infection, with the lower bound of the confidence interval at almost 90% (89%) indicating a high minimum level of efficacy.Single-dose HPV vaccination was safe with no vaccine-related SAEs.These data add to the growing suite of evidence to support single-dose HPV vaccination implementation.

Online content
Any methods, additional references, Nature Portfolio reporting summaries, source data, extended data, supplementary information, acknowledgements, peer review information; details of author contributions and competing interests; and statements of data and code availability are available at https://doi.org/10.1038/s41591-023-02658-0.Department of Global Health, University of Washington, Seattle, WA, USA. 9 Department of Obstetrics and Gynecology, University of Washington, Seattle, WA, USA. 10 Center for Clinical Research, Kenya Medical Research Institute, Nairobi, Kenya. 11Department of Epidemiology, University of Washington, Seattle, WA, USA. 12 Human Biology Division, Fred Hutchinson Cancer Center, Seattle, WA, USA. 13 University of Cincinnati, Department of Obstetrics and Gynecology, Cincinnati, OH, USA. 14Department of Laboratory Medicine and Department of Pathology, University of Washington, Seattle, WA, USA.
15 Division of Allergy and Infectious Diseases, Department of Medicine, University of Washington, Seattle, WA, USA. 16East Africa STI Laboratory, University of Washington, Mombasa, Kenya.*A list of authors and their affiliations appears at the end of the paper.e-mail: rbarnabas@mgh.harvard.eduSubgroups are defined by lab results or self-reported behavior at the enrollment visit.No adjustments for multiplicity were done.Two-sided log-rank p-values are computed for each comparison using the log-rank test.

Cumulative incidence curves for the incidence of persistent HPV in the modified intention-to-treat primary analyses.
Cumulative incidence curves were computed by vaccine group using Kaplan-Meier methods.Two-sided log-rank P values were computed for each comparison using the log-rank test.a, Cumulative incidence of persistent HPV 16/18 in the HPV 16/18 mITT cohort (n = 1,458).Four participants in the HPV 16/18 mITT cohort did not contribute a second end-point swab and thus did not contribute time at risk.b, Cumulative incidence of persistent HPV 16/18/31/33/45/52/58 in the HPV 16/18/31/33/45/52/ 58 mITT cohort (n = 615).One participant in the HPV 16/18/31/33/45/52/58 mITT cohort did not contribute a second end-point swab and thus did not contribute time at risk.

Table 4 | Incidence of persistent HPV and vaccine efficacy using cervical swabs only (mITT primary cohorts)
Post hoc analysis used cervical swabs only to ascertain end points; all self-collected swabs after month 3 were excluded.Methods are otherwise the same as described in Table 2.No multiplicity adjustments were performed.a link to the Creative Commons license, and indicate if changes were made.The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in a credit line to the material.If material is not included in the article's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.To view a copy of this license, visit http://creativecommons. org/licenses/by/4.0/.Division of Infectious Diseases, Department of Medicine, Massachusetts General Hospital, Boston, MA, USA. 2 School of Medicine, Harvard Medical School, Boston, MA, USA. 3 Department of Epidemiology, T. H. Chan Harvard School of Public Health, Boston, MA, USA. 4 Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Center, Seattle, WA, USA. 5 Public Health Sciences, Fred Hutchinson Cancer Center, Seattle, WA, USA. 6Department of Biostatistics, University of Washington, Seattle, WA, USA. 7Center for Microbiology Research, Kenya Medical Research Institute, Kisumu, Kenya.
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Extended Data Table. 5 | Summary of follow-up laboratory results by randomized group (mITT cohorts) Extended Data Table. 6 | Incidence of persistent HPV 16/18 and vaccine efficacy overall and within subgroups defined by lab results or self-reported behavior at enrollment (mITT cohort)
Subgroups are defined by lab results or self-reported behavior at the enrollment visit.No adjustments for multiplicity were done.Two-sided log-rank p-values are computed for each comparison using the log-rank test.