>> Proof-of-Principle: Efficacy of fewer than 3-doses of a bivalent HPV 16/18 vaccine against incident persistent HPV infection in Guanacaste, Costa Rica
12:00 PM - 12:15 PM
1National Cancer Institute, National Institutes of Health, Bethesda, MD, USA; 2Proyecto Epidemiológico Guanacaste, Fundación INCIENSA, San Jose, Costa Rica; 3DDL Diagnostic Laboratory, Voorburg, The Netherlands; 4Information Management Services, Inc., Rockville, MD, USA.
Background: Three-dose regimens for HPV vaccines are expensive to purchase and deliver, and often not feasible where the need is most crucial. Even in high resource regions, compliance is low.
To evaluate efficacy of two and one doses of a bivalent HPV 16/18 vaccine for the prevention of newly detected HPV16/18 one-year persistent infection.
Methods: 7,466 women (18-25 years) were randomized 1:1 to Cervarix or hepatitis A vaccine (control) and followed yearly (or semiannually if LSIL). VE was calculated after excluding women with zero post-enrolment visits or with both HPV16 and 18 DNA positivity at enrolment (155:160 HPV:Control). 383 women who received 1 dose (196:187), 801 who received 2 doses (422:379), and 5,976 who received 3 doses (2957:3010) comprised the analytic population. Median follow-up was three years, comparable by doses received and arm. Reasons for receiving <3 doses and other relevant pre- and post-randomization characteristics were balanced within dose by arm. One-year persistence was defined as two positive tests for the same HPV type in visits 10+ months apart in women negative at enrollment for that HPV type. Dose-stratified efficacies compared events in HPV to control arm; exact 95% confidence intervals were calculated.
Results: Attack rate of incident one-year persistent HPV16/18 infection in the control arm was 4.3% for 1 dose, 4.0% for 2 doses, and 3.8% for 3 doses. Vaccine efficacy for 1 dose was 100% (95%CI 57%-100%; n=8 total events), for 2 doses 82% (95%CI 43%-96%; n= 18 total events), and for 3 doses 78% (95%CI 67%-86%; n=137 total events). Results were similar for 6-month persistence.
Conclusion: Our data do not provide sufficient evidence to modify existing 3-dose schedules, but suggest that fewer than three doses may provide a high degree of protection against HPV-16/18 infection. Systematic evaluation of one- and two-dose schedules is justified.