Just 1 dose of the human papillomavirus (HPV) vaccine may provide protection against HPV-16/18 similar to the 3-dose schedule, according to results from 2 clinical trials. If the outcomes hold true in further study, the investigators said, a 1-dose approach might help overcome barriers to vaccine uptake in many regions of the world.
Researchers used data from the Costa Rica Vaccine Trial and the PATRICIA trial, which were both Phase III, double-blind, randomized controlled clinical trials of the HPV-16/18 AS04-adjuvanted vaccine in adolescent and young adult women. Women with less than 12 months of follow-up or those who were HPV-16- or HPV-18- DNA-positive at the time of enrollment were excluded from calculations. The researchers calculated the vaccine efficacy against a 1-time detection of incident HPV infections after 1, 2, or 3 doses of the vaccine.
In the cohort, 22,327 of the women received all 3 doses, 1185 received 2 doses, and 543 received 1 dose. The efficacy of the vaccine against incident HPV-16/18 infections for 3 doses was 77.0% (95% confidence interval [CI] 74.7 – 79.1), for 2 doses it was 76.0% (62.0 – 85.3), and for 1 dose it was 85.7% (70.7 – 93.7). Efficacy of the vaccine against incident HPV-31/33/45 infections was 59.7% (56.0 – 63.0) for 3 doses, 37.7% (12.4 – 55.9) for 2 doses, and 36.6% (-5.4 to 62.2) for 1 dose. The investigators noted that some of the outcomes might have resulted from undetected infections present before vaccination, which explains why efficacy estimates for this endpoint are generally lower than those for persistent infection.
For women who received 2 doses, the vaccine efficacy against incident HPV-16/18 was 75.3% (54.2 – 87.5) when the second dose was administered at 1 month; it was 82.6% (42.3 – 96.1) for those who received the second dose at 6 months. For HPV-31/33/45, vaccine efficacy for those who received their second dose at 6 months (68.1%, 27.0–87.0) was similar to those who received all 3 doses.
The investigators found that in women aged 15 to 25, at 4 years after vaccination, 1 or 2 doses of HPV16/18 vaccine appeared to provide protection similar to a 3-dose schedule. For those receiving 2 doses, having the 2 shots separated by 6 months provided some extra cross-protection. They believe that further research is warranted about the efficacy of 1 dose for protecting against HPV-16/18.