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Quadrivalent HPV Vaccine Produced in Yeast Achieves Over 99% Seroconversion in Females Aged 9–45
A randomized, double-blind, placebo-controlled Phase II trial found seroconversion rates exceeding 99% for all four HPV types (6, 11, 16, and 18) in seronegative participants following a three-dose regimen of a quadrivalent HPV vaccine manufactured using the Hansenula polymorpha yeast expression system. Immune responses in the 9–17 age group were non-inferior to those in the 18–45 age group, and no vaccine-related serious adverse events were recorded.
What Was Studied
This study evaluated whether a quadrivalent recombinant HPV vaccine produced in the yeast Hansenula polymorpha generates adequate and safe immune responses across a broad age range of healthy females, and whether younger adolescents mount antibody responses at least as strong as those in older participants — a key regulatory criterion for extending vaccine approval to younger age groups.
How It Was Studied
This was a randomized, double-blind, placebo-controlled Phase II non-inferiority trial enrolling 1,800 healthy females aged 9 to 45 years, allocated to vaccine or placebo in a 2:1 ratio. Participants received three intramuscular doses at months 0, 2, and 6, following a standard HPV vaccination schedule. Neutralizing antibody titers against HPV types 6, 11, 16, and 18 were measured using a pseudovirus-based neutralization assay (PBNA) on serum samples collected before the first dose and 30 days after the third dose. The immunobridging comparison between the 9–17 and 18–45 age cohorts used a pre-specified non-inferiority margin of −10% in seroconversion rates, with a one-sided significance level of 2.5%. Safety monitoring included adverse reactions within 30 days after each dose, as well as surveillance for pregnancies and serious adverse events throughout the study period.
What Was Observed
- Near-complete seroconversion in seronegative participants: Among those with no pre-existing antibodies to any of the four HPV types, seroconversion rates 30 days after the third dose reached 100% for HPV 6, 99.82% for HPV 11, 100% for HPV 16, and 99.73% for HPV 18 — indicating that the vaccine consistently generated a detectable immune response in virtually all susceptible recipients.
- Substantial antibody boosting in seropositive participants: Among participants who had pre-existing antibodies at baseline, more than 91% achieved at least a 4-fold increase in neutralizing antibody titers for each of the four HPV types, demonstrating that prior exposure did not blunt vaccine-induced responses.
- Adolescent immune response met non-inferiority threshold: Seroconversion rates in the 9–17-year-old cohort were confirmed non-inferior to those in the 18–45-year-old cohort, using the pre-specified margin, supporting the immunobridging rationale for including younger adolescents in future indications.
- Favorable safety profile across all participants: The three-dose regimen was well tolerated, with no vaccine-related serious adverse events reported in either age group across the full study observation period.
Why This Matters
The vaccine’s production in the Hansenula polymorpha expression system represents a distinct manufacturing platform whose immunogenicity and safety profile required dedicated clinical validation across the intended age range. The demonstration of robust neutralizing antibody responses — with seroconversion exceeding 99% in seronegative individuals — alongside a confirmed non-inferior response in adolescents and an absence of serious vaccine-related harm, provides the clinical foundation needed to advance this candidate into Phase III evaluation for broader HPV prevention use.
How to Read This Result
As a Phase II immunogenicity and safety trial, this study was not powered or designed to assess clinical endpoints such as prevention of HPV infection or cervical disease, so the practical protective benefit of this vaccine remains to be established in larger, longer-term trials.
Limitations
The abstract does not explicitly report study limitations.