Incomplete HPV vaccine schedules may confer similar levels of protection

1. In this combined post-hoc analysis of two phase 3, double-blind randomized trials, the bivalent HPV-16/18 vaccine AS04 was effective and conferred similar levels of protection to women after 3, 2, or 1 doses.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Prevention against cervical cancer with 3 doses of HPV vaccine can be challenging, especially in resource-limited settings where the burden of cervical cancer is greatest. This study assessed the efficacy of HPV vaccine regimens comprised of fewer than 3 doses using data compiled from 2 previous studies. In these studies, women were randomized to either receive a control vaccine or 3 doses of the bivalent AS04-adjuvanted HPV-16/18 vaccine. However, some women only received 1 or 2 doses due to a variety of reasons (such as pregnancy). In this post-hoc analysis, efficacy against one-time incident HPV infections after all 3 doses was compared to efficacy after receiving only 1 or 2 doses. Vaccination with the 3, 2, and 1-dose regimens demonstrated 77.0%, 76.0%, and 85.7% efficacy, respectively. As the fewer-dose regimens demonstrated similar levels of protection, the study raises the consideration of how best to allocate limited resources to maximize herd immunity, while preserving individual protection. Such a question can be best addressed with a future study that directly assesses the one-dose efficacy of the HPV-16/18 vaccine. This study was well designed and adequately powered with data from two phase 3 randomized control trials. However, women were non-randomly assigned to the dosage groups in the final analysis and therefore may have had differing levels of risk for HPV infection.

The study was funded by US National Cancer Institute, National Institutes of Health Office of Research on Women’s Health, and Ministry of Health of Costa Rica (CVT); GlaxoSmithKline Biologicals SA (PATRICIA).

Click to read the study, published today in The Lancet Oncology

Relevant Reading: Number of Human Papillomavirus Vaccine Doses and Condyloma

In-Depth [randomized controlled trial]: This is a post-hoc analysis that assessed the efficacy of the bivalent AS04-adjuvanted HPV-16/18 vaccine regimens after 3, 2, or 1 doses, based on previously collected data from the Costa Rica Vaccine and PATRICIA trials – both of which were phase 3, double-blind, randomized controlled trials. In both trials, women were randomized to receive either a vaccine or 3 doses of the HPV-16/18 vaccine. However, some women only received 1 or 2 doses. The primary endpoint was one-time detection of first HPV-16/18 infection.

Overall, 22,327 women included in the analysis received 3 doses, 1,185 received 2, and 543 received 1 dose of the HPV-16/18 vaccine. Calculated post-hoc vaccine efficacies against one-time incident HPV-16/18 infection after receiving 3, 2, or 1 dose(s) were 77.0% (95% CI 74.7-79.1), 76.0% (95% CI 62.0-85.3), and 85.7% (95% CI 70.7-93.7), respectively. For women in the two-dose group, vaccine efficacy was 75.3% (95% CI 54.2-87.5) if the second dose was administered 1 month later, and 82.6% (95% CI 42.3-96.1) if the second dose was administered 6 months later.

Image: PD/CDC

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