Human papillomavirus (HPV) type 16 and type 18 antibody concentrations after a single dose of bivalent HPV vaccine in girls aged 9-14 years compared with three doses of quadrivalent HPV vaccine in women aged 18-25 years in Costa Rica (PRIMAVERA): a non-randomised, open-label, immunobridging, non-inferiority trial.

backgroundIn 2022, WHO recommended single-dose human papillomavirus (HPV) vaccination as an alternative schedule to multidose regimens. To provide evidence to support approval of a single-dose indication for the AS04-adjuvanted bivalent HPV vaccine (Cervarix, GlaxoSmithKline), we investigated whether the immune response to a single dose of the bivalent vaccine in girls aged 9-14 years was non-inferior to the immune response to three doses of the quadrivalent HPV vaccine (Gardasil-4, Merck) in women aged 18-25 years, a dose and population combination with demonstrated efficacy.

methodsThis non-randomised, open-label, immunobridging trial enrolled girls aged 9-14 years and women aged 18-25 years in Guanacaste Province, Costa Rica. Healthy girls aged 9-14 years received one dose of bivalent HPV vaccine, whereas healthy women aged 18-25 years received three doses of quadrivalent HPV vaccine at 0, 2, and 6 months. The primary endpoint was geometric mean concentrations (GMCs) of HPV-specific serum antibodies measured by a validated virus-like-particle-based ELISA assay at 36 months. The per-protocol cohort included participants who received the correct number of doses within the predefined vaccination windows, had blood collected at the 36-month study visit for the final analysis, were seronegative at baseline for the specified HPV type, and did not receive additional HPV vaccine doses outside the study. Non-inferiority was declared when the lower bound of the 96% CI for the GMC ratio was greater than or equal to 0·67 for HPV-16 and HPV-18. Seropositivity was a secondary objective. Safety was analysed in the total vaccinated population. This trial is registered with ClinicalTrials.gov, NCT03728881, and is complete.

findingsBetween April 1 and Aug 16, 2019, 620 girls and 620 women were enrolled and received their first HPV vaccination. After exclusions, 539 girls and 366 women were HPV-16 seronegative at enrolment and were included in the HPV-16 per-protocol cohort; 523 girls and 373 women were HPV-18 seronegative at enrolment and were included in the HPV-18 per-protocol cohort. At 36 months, the HPV-16 GMC was 21·4 international units (IU)/mL (95% CI 19·7-23·3) in girls in the single-dose bivalent vaccine group and 42·9 IU/mL (95% CI 38·9-47·3) in women in the three-dose quadrivalent vaccine group, resulting in a GMC ratio of 0·50 (96% CI 0·44-0·57); the HPV-18 GMC was 8·0 IU/mL (95% CI 7·4-8·8) in girls in the single-dose bivalent vaccine group and 7·2 IU/mL (95% CI 6·4-8·1) in women in the three-dose quadrivalent vaccine group, resulting in a GMC ratio of 1·11 (96% CI 0·95-1·29). At 36 months, 538 (99·8%, 95% CI 99·1-100) of 539 girls in the single-dose bivalent vaccine group were seropositive for HPV-16 compared with 366 (100%, 99·2-100) of 366 women in the three-dose quadrivalent vaccine group (p=1·00). The proportion of participants who were seropositive for HPV-18 was higher in the single-dose bivalent vaccine group (517 [98·9%, 95% CI 97·6-99·5] of 523 girls) than in the three-dose quadrivalent vaccine group (358 [96·0%, 93·6-97·6] of 373 women; p=0·0065). Two serious adverse events were reported in 620 girls and 13 serious adverse events were reported in 620 women; all serious adverse events were deemed to be unrelated to HPV vaccination.

interpretationNon-inferior antibody responses for the single-dose bivalent HPV vaccine were seen for HPV-18 but not HPV-16, which would be insufficient evidence to motivate regulatory change, even though seropositivity approached 100% in the follow-up phase and the observed antibody concentrations were similar to protective levels seen in previous trials. Trials that directly evaluate protection afforded by single-dose HPV vaccination against persistent HPV infection will definitively address the level of protection afforded by single-dose HPV vaccination.

fundingNational Cancer Institute, Cancer Research UK, and the Gates Foundation. TRANSLATION: For the Spanish translation of the abstract see Supplementary Materials section.